rs422: Support runtime re-init of the GPS receiver
Currently if the GPS receiver side doesn't have power, init will fail and never recover without a reboot.
This is because without power on that side, we can't talk to the I2C IO expander on the isolated side to initialize it and set up the RS422 transceiver ...
Solution is that if we haven't seen NMEA messages in a few seconds, try to re-init the I2C IO expander (default state on reset/power loss is everything disabled to be safe).
One thing to pay attention to is that I2C is slow. And the current I2C driver code is blocking, so we'd need to check the init sequence isn't too long and doesn't block the main loop processing for too long which would cause USB over/underflows ...