dt-bindings: pwm: rcar: Add r8a774a1 support

Document RZ/G2M (R8A774A1) SoC bindings.
Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

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

@@ -5,6 +5,7 @@ Required Properties:
  - "renesas,pwm-r8a7743": for RZ/G1M
  - "renesas,pwm-r8a7744": for RZ/G1N
  - "renesas,pwm-r8a7745": for RZ/G1E
+ - "renesas,pwm-r8a774a1": for RZ/G2M
  - "renesas,pwm-r8a7778": for R-Car M1A
  - "renesas,pwm-r8a7779": for R-Car H1
  - "renesas,pwm-r8a7790": for R-Car H2