dt-bindings: bus: rsb: Add H616 compatible string

Add the obvious compatible name to the existing RSB binding, and pair
it with the existing A23 fallback compatible string, as the devices are
compatible.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210127172500.13356-15-andre.przywara@arm.com