serial_common.c/h. decouple runtime_config from serial ports. decouple
buzzer from serial ports. decouple opening of the main serial port from
the msp code. decouple serial rx providers from runtime_config. rename
core_t to serialPorts_t since it only contained serial ports. It's now
clear which files use serial ports based on the header files they
include.
remove dependency on board.h and mw.h on a few files.
Moved rx configuration paramaters into rxConfig in order to remove the
dependency on config_t from the sbus rx code - sumd/spektrum to follow.
Avoided use of YAW/PITCH/ROLL in some files since those constants are
from an unrelated enum type.
Replaced some magic numbers with constants to remove comments and
improve code readability.
Note, due to the tight coupling and global variable usage it was
difficult to create a smaller commit.
