dt-bindings: serial: sh-sci: Document r8a78000 bindings

dt-bindings: serial: sh-sci: Document r8a78000 bindings

R-Car X5H (R8A78000) SoC has the R-Car Gen5 compatible SCIF and
HSCIF ports, so document the SoC specific bindings.

[Kuninori: tidyup for upstreaming]

Signed-off-by: Nghia Nguyen <nghia.nguyen.jg@renesas.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: "Rob Herring (Arm)" <robh@kernel.org>
Link: https://lore.kernel.org/r/87ecuxdggq.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>