devicetree: add DT_COMPAT_ON_BUS()

And implement DT_ANY_INST_ON_BUS() in terms of it.

This makes some error messages quite a bit shorter by avoiding
UTIL_LISTIFY(), which has a nasty temper and tends to explode if not
treated gently.

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