esp32s2: suspend UART output using XOFF before entering light sleep
esp32s2: suspend UART output using XOFF before entering light sleep

Same logic as for the ESP32, except two changes:

* need to set UART_SW_FLOW_CON_EN bit for UART_FORCE_XOFF to take
  effect
* need to check if the peripheral is not clockgated and out of reset

espressif/esp-idf,espressif/esp-idf,espressif/esp-idf,espressif/esp-idf