dt-bindings: timer: renesas: tmu: Document r8a774a1 bindings

Document RZ/G2M (R8A774A1) SoC in the Renesas TMU bindings.
Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1560258401-9517-6-git-send-email-fabrizio.castro@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

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

@@ -10,6 +10,7 @@ Required Properties:
 
   - compatible: must contain one or more of the following:
     - "renesas,tmu-r8a7740" for the r8a7740 TMU
+    - "renesas,tmu-r8a774a1" for the r8a774A1 TMU
     - "renesas,tmu-r8a774c0" for the r8a774C0 TMU
     - "renesas,tmu-r8a7778" for the r8a7778 TMU
     - "renesas,tmu-r8a7779" for the r8a7779 TMU