dt-bindings: serial: renesas,scif: Document r8a779a0 bindings

dt-bindings: serial: renesas,scif: Document r8a779a0 bindings

R-Car V3U (R8A779A0) SoC also has the R-Car Gen3 compatible
SCIF ports, so document the SoC specific bindings.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1605250296-30570-1-git-send-email-yoshihiro.shimoda.uh@renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>