dt-bindings: timer: renesas, cmt: Document r8a77470 CMT support

Document SoC specific compatible strings for r8a77470. No driver change
is needed as the fallback strings will activate the right code.
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Documentation/devicetree/bindings/timer/renesas,cmt.txt

@@ -28,6 +28,8 @@ Required Properties:
     - "renesas,r8a7744-cmt1" for the 48-bit CMT1 device included in r8a7744.
     - "renesas,r8a7745-cmt0" for the 32-bit CMT0 device included in r8a7745.
     - "renesas,r8a7745-cmt1" for the 48-bit CMT1 device included in r8a7745.
+    - "renesas,r8a77470-cmt0" for the 32-bit CMT0 device included in r8a77470.
+    - "renesas,r8a77470-cmt1" for the 48-bit CMT1 device included in r8a77470.
     - "renesas,r8a7790-cmt0" for the 32-bit CMT0 device included in r8a7790.
     - "renesas,r8a7790-cmt1" for the 48-bit CMT1 device included in r8a7790.
     - "renesas,r8a7791-cmt0" for the 32-bit CMT0 device included in r8a7791.