spi: renesas,sh-msiof: Add r8a779g0 support

Document support for the Clock-Synchronized Serial Interface with FIFO
(MSIOF) in the Renesas R-Car V4H (R8A779G0) SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/a840ca8487cfd612fae2b20c98e93ae7c7f50ef4.1664204638.git.geert+renesas@glider.be


Signed-off-by: Mark Brown <broonie@kernel.org>