spi: renesas,sh-msiof: Add r8a779a0 support

Document R-Car V3U (R8A779A0) SoC bindings.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20210108103522.2025880-1-geert+renesas@glider.be


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