boards: bbc_microbit: reference board variations

The original v1.3 had MMA8653+MAG3110, but v1.5 has verified LSM303AGR
and theoretical FXOS8700.  Add the v1.5 variant 1 nodes in disabled
form; they can be enabled through overlays.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
1 file changed