boards: bbc_microbit_v2: add missing i2c0 compatible

The board's main I2C bus controller doesn't have a compatible set, so
it's not detected as an I2C bus at all.

This breaks the build when trying to build the samples/sensor/lis2dh
application with the lis2dh sensor on that bus.

Fixes: #32420
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>