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.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>