esp32s2: Reserve UART pins only if DEBUG=1 is set to address issue 3811

[BennyE]

This addresses issue #3811

Same patch for all esp32s2 boards. Tested on featherS2 (see screenshot below).

Python code for test:

import board
import busio
uart = busio.UART(board.TX, board.RX, baudrate=115200)
uart.write(bytes("Test123", "utf8"))

[BennyE]

@tannewt please check if my changes in the Makefile are valid. It works as expected, thanks for the due-dilligence. I didn't realise that the debug was enabled/disabled via sdkconfig files and DEBUG=1 on make command didn't set the CFLAG.

[tannewt]

Looks great! Thanks!