dt-bindings: display: simple-bridge: Add corpro,gm7123 compatible

The corpro,gm7123 was in use in a DT but was never properly documented,
let's add it.

Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210721140424.725744-12-maxime@cerno.tech