esp32: Add MICROPY_HW_ENABLE_UART_REPL and enable on generic S2/S3.

Some S2/S3 modules don't use the native USB interface but instead have an
external USB-UART.  To make the GENERIC_S3/S3 firmware work on these boards
the UART REPL is enabled in addition to the native USB CDC REPL.

Fixes issues #8418 and #8524.

Signed-off-by: Damien George <damien@micropython.org>

ports/esp32/main.c

@@ -92,7 +92,8 @@ void mp_task(void *pvParameter) {
     usb_init();
     #elif CONFIG_ESP_CONSOLE_USB_SERIAL_JTAG
     usb_serial_jtag_init();
-    #else
+    #endif
+    #if MICROPY_HW_ENABLE_UART_REPL
     uart_stdout_init();
     #endif
     machine_init();