esp32/boards/ESP32_GENERIC_C3: Enable UART REPL.

This should have been added in 4815af75
when the variants were combined. The original non-USB variant got this
implicitly, and therefore was not in mpconfigvariant.h
Signed-off-by: NJim Mussared <jim.mussared@gmail.com>

ports/esp32/boards/ESP32_GENERIC_C3/mpconfigboard.h

@@ -6,3 +6,6 @@
 #define MICROPY_HW_ENABLE_SDCARD            (0)
 #define MICROPY_PY_MACHINE_DAC              (0)
 #define MICROPY_PY_MACHINE_I2S              (0)
+
+// Enable UART REPL for modules that have an external USB-UART and don't use native USB.
+#define MICROPY_HW_ENABLE_UART_REPL         (1)