media: dt-bindings: rcar-vin: Document compatibility string for R8A77470

When adding the compatibility string for R8A77470 (RZ/G1C) to the
rcar-vin driver the string was never documented in the bindings, add it
now.
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/devicetree/bindings/media/renesas,vin.txt

@@ -13,6 +13,7 @@ on Gen3 and RZ/G2 platforms to a CSI-2 receiver.
    - "renesas,vin-r8a7743" for the R8A7743 device
    - "renesas,vin-r8a7744" for the R8A7744 device
    - "renesas,vin-r8a7745" for the R8A7745 device
+   - "renesas,vin-r8a77470" for the R8A77470 device
    - "renesas,vin-r8a774a1" for the R8A774A1 device
    - "renesas,vin-r8a774b1" for the R8A774B1 device
    - "renesas,vin-r8a774c0" for the R8A774C0 device