GPS support was implemented incorrectly for the ThinkNode M3. The reset
pin was being driven when it should be left floating for this unit. The
enable pin also wasn't being picked up by `MicroNMEALocationProvider`
because of a mismatch in constant naming conventions. I did a general
cleanup of the GPS and ThinkNode M3 bring-up code so that constant names
line up and "*_ACTIVE" constants are used consistently vs hardcoding
`HIGH`/`LOW`. After making these changes, serial data immediately starts
streaming in from the NMEA on boot and GPS detection just works.
LED handling was also not quite right for the ThinkNode M3. The LoRa TX
LED was being driven high to turn it on when it should actually be
driven low. I changed the code to use the `LED_STATE_ON` constant and
also added a little code to the shutdown path to properly make sure that
all LEDs are turned off.
Tested and confirmed working on real hardware.
Resolves both #1864 and #2879.
Naomi Smith