media: dt-bindings: media: meson-ao-cec: add SM1 compatible

Add AO-CEC compatible string for the Amlogic SM1 SoC family,
a derivate of the G12A AO-CECB controller.

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>