media: dt-bindings: media: i2c: Add bindings for IMI RDACM2x

The IMI RDACM20 and IMI RDACM21 are Gigabit Multimedia Serial Link
(GMSL) camera capable of transmitting video and I2C control messages on
a coax cable physical link for automotive applications.

Document their device tree bindings.

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>