Chip-select and SPI initialization uses the new config, whereas the drivers
still use the existing defines.
The configuration in board_config.h can be removed after all drivers are
updated.
-moved rc.mavlink to the boards optional rc additions (now it's called rc.board_mavlink) to handle board specific mavlink needs (mavlink over usb, ethernet, additional streams, etc.)
-mavlink module will be responsible to usb defaults, therefore less args are needed to be passed to mavlink module if one wants to use mavlink over usb.
-the way to check if connection is usb is by it's designated variable and not by config mode.