rs422: Merge as much of the gateware in master as possible
Currently the gateware for the RS422 mode is another branch. It's just too big to have dual channel + hw support for it in the same build.
Either try to make it a build option, or reduce size of the gateware to make it fit.
ATM we create a whole different UART but technically we could just use the GPS uart and re-route the IO since the on-board GPS isn't used when rs422 mode is used.
This wouldn't support a possible future GPS 02/03 emulation mode but that's a problem for the future. (Although thinking about it, it could actually since after init we never TX to the onboard GPS and we never RX anything on the rs422 ... so we could have the same uart split: rx from onboard gps and tx to the RBS ... we just need to keep the onboard gps at 9600 or support different tx/rx baudrates)