serial: sh-sci: Document r8a77470 bindings

RZ/G1C (R8A77470) SoC also has the R-Car gen2 compatible SCIF and HSCIF
ports, so document the SoC specific bindings.
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/renesas,sci-serial.txt

@@ -17,6 +17,8 @@ Required properties:
     - "renesas,scifa-r8a7745" for R8A7745 (RZ/G1E) SCIFA compatible UART.
     - "renesas,scifb-r8a7745" for R8A7745 (RZ/G1E) SCIFB compatible UART.
     - "renesas,hscif-r8a7745" for R8A7745 (RZ/G1E) HSCIF compatible UART.
+    - "renesas,scif-r8a77470" for R8A77470 (RZ/G1C) SCIF compatible UART.
+    - "renesas,hscif-r8a77470" for R8A77470 (RZ/G1C) HSCIF compatible UART.
     - "renesas,scif-r8a7778" for R8A7778 (R-Car M1) SCIF compatible UART.
     - "renesas,scif-r8a7779" for R8A7779 (R-Car H1) SCIF compatible UART.
     - "renesas,scif-r8a7790" for R8A7790 (R-Car H2) SCIF compatible UART.