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.
- it does nothing useful
- increases boot time by 2 seconds on pixhawk 4 due to a poll timeout:
IST8310 on I2C bus 3 at 0x0e (bus: 100 KHz, max: 400 KHz)
WARN [ist8310] ERROR: TIMEOUT 2
-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.
