The ESP32 RMT peripheral has hardware support for a carrier frequency, and
this commit exposes it to Python with the keyword arguments carrier_freq
and carrier_duty_percent in the constructor. Example usage:
r = esp32.RMT(0, pin=Pin(2), clock_div=80, carrier_freq=38000, carrier_duty_percent=50)
This commit consolidates a number of check_esp_err functions that check
whether an ESP-IDF return code is OK and raises an exception if not. The
exception raised is an OSError with the error code as the first argument
(negative if it's ESP-IDF specific) and the ESP-IDF error string as the
second argument.
This commit also fixes esp32.Partition.set_boot to use check_esp_err, and
uses that function for a unit test.