arm64: dts: renesas: r8a779g0: Add RPC node

Add a device node for the SPI Multi I/O Bus Controller (RPC-IF) on the
Renesas R-Car V4H (R8A779G0) SoC.

Signed-off-by: Hai Pham <hai.pham.ud@renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/6da7a035d56a943336f68dc0da77a47dba3dd69e.1665583435.git.geert+renesas@glider.be