sys.platform not present for ESP32-S2 boards like FeatherS2

[kevinjwalters]

A new FeatherS2 (from @UnexpectedMaker) which comes with 6.0.0 does not have sys.platform:

Adafruit CircuitPython 6.0.0 on 2020-11-16; FeatherS2 with ESP32S2
>>> import sys
>>> dir(sys)
['__class__', '__name__', 'argv', 'byteorder', 'exit', 'implementation', 'maxsize', 'modules', 'path', 'print_exception', 'stderr', 'stdin', 'stdout', 'version', 'version_info']
>>> sys.version
'3.4.0'
>>> sys.platform
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'platform'

@jepler mentions in land of Discord

it looks like this is missing because the port doesn't define a macro. It would need to be similar to nrf: ports/nrf/mpconfigport.h:#define MICROPY_PY_SYS_PLATFORM "nRF52840".

referring to https://github.com/adafruit/circuitpython/blob/main/ports/esp32s2/mpconfigport.h which seems a lot small than the nrf and atmel-samd ones.

[anecdata]

Added in #3954. Closing.