Add ability to initiate CRSF receiver binding from QGroundControl or
the NSH console. When MAV_CMD_START_RX_PAIR is received with
RC_TYPE_CRSF, the driver sends the CRSF bind command frame over UART.
Binding is rejected when armed or on singlewire configurations.
Also adds RC_TYPE and RC_SUB_TYPE constants to VehicleCommand.msg and
replaces magic numbers in DsmRc and RCInput drivers.
Based on PX4/PX4-Autopilot#23294.
2bf50badf4