arch: riscv: stacktrace: user thread stack bound check is wrong

[ycsin]

Describe the bug
The calculation of the stack bounds is wrong according to the riscv's arch.h:

 +------------+ <- thread.arch.priv_stack_start
 | Guard      | } Z_RISCV_STACK_GUARD_SIZE
 +------------+
 | Priv Stack | } CONFIG_PRIVILEGED_STACK_SIZE
 +------------+ <- thread.arch.priv_stack_start +
                   CONFIG_PRIVILEGED_STACK_SIZE +
                   Z_RISCV_STACK_GUARD_SIZE

The start of the privilege stack should be:

thread.arch.priv_stack_start + Z_RISCV_STACK_GUARD_SIZE

Instead of

thread.arch.priv_stack_start - CONFIG_PRIVILEGED_STACK_SIZE

This resulted in empty call trace when the exception happens in a userspace thread.

To Reproduce
Steps to reproduce the behavior:

1. Check out v3.7.0
2. west build -b qemu_riscv64 -p auto -t run -T zephyr/tests/kernel/mem_protect/userspace/kernel.memory_protection.userspace
3. Exception message of test_unimplemented_syscall doesn't contain call traces:

START - test_unimplemented_syscall
E: Unimplemented system call
E: call trace:
E:
E: >>> ZEPHYR FATAL ERROR 3: Kernel oops on CPU 0
E: Current thread: 0x80020ba8 (test_unimplemented_syscall)
Caught system error -- reason 3
System error was expected
 PASS - test_unimplemented_syscall in 0.004 seconds

Expected behavior
There should be call traces:

START - test_unimplemented_syscall
E: Unimplemented system call
E: call trace:
E:       0: ra: 00000000800034b6
E:       1: ra: 00000000800005d0
E:       2: ra: 0000000080003660
E:       3: ra: 00000000800029e0
E:       4: ra: 00000000800029fa
E:       5: ra: 0000000080002b08
E:       6: ra: 0000000080002b16
E:       7: ra: 000000008000d51e
E:
E: >>> ZEPHYR FATAL ERROR 3: Kernel oops on CPU 0
E: Current thread: 0x80020ba8 (test_unimplemented_syscall)
Caught system error -- reason 3
System error was expected
 PASS - test_unimplemented_syscall in 0.006 seconds

Impact
No call traces in userspace

Environment (please complete the following information):

• Commit SHA or Version used: Zephyr v3.7.0

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[ycsin]

Fixed in #75564 and backported in #76380