dt-bindings: pwm: Add R-Car M3-W device tree bindings

Add device tree bindings for the PWM controller found on R-Car M3-W SoCs.
Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/renesas,pwm-rcar.txt

@@ -8,6 +8,7 @@ Required Properties:
  - "renesas,pwm-r8a7791": for R-Car M2-W
  - "renesas,pwm-r8a7794": for R-Car E2
  - "renesas,pwm-r8a7795": for R-Car H3
+ - "renesas,pwm-r8a7796": for R-Car M3-W
 - reg: base address and length of the registers block for the PWM.
 - #pwm-cells: should be 2. See pwm.txt in this directory for a description of
   the cells format.