dt-bindings: clock: renesas,cpg-mssr: Document r8a779g0

Add binding documentation for the R-Car V4H (R8A779G0) Clock Pulse
Generator.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220420084255.375700-7-yoshihiro.shimoda.uh@renesas.com


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