dt-bindings: power: renesas,rcar-sysc: Document r8a779a0 SYSC bindings

Document bindings for the R-Car V3U (aka R8A779A0) SYSC block.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/1599470390-29719-4-git-send-email-yoshihiro.shimoda.uh@renesas.com


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