Torch needs NMEA/RTCM output over serial

There may be some installations where transmission over Bluetooth is not desired, and a wired connection for GNSS data is wanted. This is not an issue for platforms that have multiple serial interfaces (you could, say, just connect straight to the ZED on the EVK). But on devices that have only one USB connection (ie, Torch) we may want have a mode where GNSS data is piped to the USB Serial port.