media: dt-bindings: media: meson-ao-cec: Add G12A AO-CEC-B Compatible

The Amlogic G12A embeds a second CEC controller named AO-CEC-B, and
the other one is AO-CEC-A described by the current bindings.

The register interface is very close but the internal architecture
is totally different.

The other difference is the clock source, the AO-CEC-B takes the
"oscin", the Always-On Oscillator clock, as input and embeds a
dual-divider clock divider to provide the precise 32768Hz base
clock for CEC communication.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>