media: dt-bindings: media: rcar_vin: add device tree support for r8a7744

Add compatible strings for r8a7744. No driver change is needed as
"renesas,rcar-gen2-vin" will activate the right code.However, it is good
practice to document compatible strings for the specific SoC as this
allows SoC specific changes to the driver if needed, in addition to
document SoC support and therefore allow checkpatch.pl to validate
compatible string values.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Acked-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>