[DellEMC]: EEPROM decoder for S6000, S6000-ON (#4718)

**- Why I did it**

For decoding system EEPROM of S6000 based on Dell offset format and S6000-ON’s system EEPROM in ONIE TLV format.

**- How I did it**

- Differentiate between S6000 and S6000-ON using the product name available in ‘dmi’  ( “/sys/class/dmi/id/product_name” )
- For decoding S6000 system EEPROM in Dell offset format and updating the redis DB with the EEPROM contents, added a new class ‘EepromS6000’ in eeprom.py, 
- Renamed certain methods in both Eeprom, EepromS6000 classes to accommodate the plugin-specific methods.

**- How to verify it**

- Use 'decode-syseeprom' command to list the system EEPROM details.
- Wrote a python script to load chassis class and call the appropriate methods.

UT Logs: [S6000_eeprom_logs.txt](https://github.com/Azure/sonic-buildimage/files/4735515/S6000_eeprom_logs.txt), [S6000-ON_eeprom_logs.txt](https://github.com/Azure/sonic-buildimage/files/4735461/S6000-ON_eeprom_logs.txt)
Test script: [eeprom_test_py.txt](https://github.com/Azure/sonic-buildimage/files/4735509/eeprom_test_py.txt)

device/dell/x86_64-dell_s6000_s1220-r0/plugins/eeprom.py

@@ -10,13 +10,21 @@
 #############################################################################
 
 try:
-    from sonic_eeprom import eeprom_tlvinfo
-except ImportError, e:
-    raise ImportError (str(e) + "- required module not found")
+    from sonic_eeprom.eeprom_tlvinfo import TlvInfoDecoder
+    from sonic_platform.eeprom import EepromS6000
+except ImportError as e:
+    raise ImportError(str(e) + "- required module not found")
 
 
-class board(eeprom_tlvinfo.TlvInfoDecoder):
+class board(object):
 
-    def __init__(self, name, path, cpld_root, ro):
-        self.eeprom_path = "/sys/class/i2c-adapter/i2c-10/10-0053/eeprom"
-        super(board, self).__init__(self.eeprom_path, 0, '', True)
+    def __new__(cls, name, path, cpld_root, ro):
+        eeprom_path = "/sys/class/i2c-adapter/i2c-10/10-0053/eeprom"
+
+        with open("/sys/class/dmi/id/product_name", "r") as fd:
+            board_type = fd.read()
+
+        if 'S6000-ON' in board_type:
+            return TlvInfoDecoder(eeprom_path, 0, '', True)
+        else:
+            return EepromS6000(is_plugin=True)

platform/broadcom/sonic-platform-modules-dell/s6000/sonic_platform/chassis.py

@@ -15,7 +15,7 @@
     import subprocess
     from sonic_platform_base.chassis_base import ChassisBase
     from sonic_platform.sfp import Sfp
-    from sonic_platform.eeprom import Eeprom
+    from sonic_platform.eeprom import Eeprom, EepromS6000
     from sonic_platform.fan import Fan
     from sonic_platform.psu import Psu
     from sonic_platform.thermal import Thermal
@@ -68,7 +68,14 @@ def __init__(self):
         # Get Transceiver status
         self.modprs_register = self._get_transceiver_status()
 
-        self._eeprom = Eeprom()
+        with open("/sys/class/dmi/id/product_name", "r") as fd:
+            board_type = fd.read()
+
+        if 'S6000-ON' in board_type:
+            self._eeprom = Eeprom()
+        else:
+            self._eeprom = EepromS6000()
+
         for i in range(MAX_S6000_FAN):
             fan = Fan(i)
             self._fan_list.append(fan)
@@ -138,7 +145,7 @@ def get_name(self):
         Returns:
             string: The name of the chassis
         """
-        return self._eeprom.modelstr()
+        return self._eeprom.get_model()
 
     def get_presence(self):
         """
@@ -154,15 +161,15 @@ def get_model(self):
         Returns:
             string: Model/part number of chassis
         """
-        return self._eeprom.part_number_str()
+        return self._eeprom.get_part_number()
 
     def get_serial(self):
         """
         Retrieves the serial number of the chassis (Service tag)
         Returns:
             string: Serial number of chassis
         """
-        return self._eeprom.serial_str()
+        return self._eeprom.get_serial()
 
     def get_status(self):
         """
@@ -181,7 +188,7 @@ def get_base_mac(self):
             A string containing the MAC address in the format
             'XX:XX:XX:XX:XX:XX'
         """
-        return self._eeprom.base_mac_addr()
+        return self._eeprom.get_base_mac()
 
     def get_serial_number(self):
         """
@@ -191,7 +198,7 @@ def get_serial_number(self):
             A string containing the hardware serial number for this
             chassis.
         """
-        return self._eeprom.serial_number_str()
+        return self._eeprom.get_serial_number()
 
     def get_system_eeprom_info(self):
         """