This avoids the need for recalibration, and also cleans up other driver
ID's (merge separate accel/gyro).
The SPI address was previously set to a board-specific (arbitrary) value,
and is now set to 0. This will allow extending for multiple sensors of the
same type on the same bus.
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.
Beat Küng