Allow all buad rates via VCP since baud rate doesn't matter for VCP.
Separate UBLOX GPS SBAS configuration from GPS init.

Extracted NMEA and UBLOX code from the GPS hardware init method into
separate methods.  Introduced a state for changing baud rate rather than
re-using state_position.
Allow GPS SBAS mode to be configurable.

It was noticed that GPS startup time increased when the change was made
from using EGNOS by default to using AUTO by default.

The default is still AUTO but faster GPS startup times may be achieved
by telling the GPS receiver what region you are in.

This also removes more unfinished MTK gps provider support.