dt-bindings: serial: renesas,scif: Document r8a779f0 bindings

R-Car S4-8 (R8A779F0) SoC has the R-Car Gen4 compatible SCIF ports,
so document the SoC specific bindings.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20211209070817.1223888-2-yoshihiro.shimoda.uh@renesas.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>