ARM: dts: renesas: Add Renesas R8A779H0 V4M DT extras

Add Renesas R8A779H0 V4M DT extras for U-Boot.

Until the RPC node becomes part of main DT, keep it here as
an extension so that board code can enable and use the RPC
to access SPI NOR.

Signed-off-by: Hai Pham <hai.pham.ud@renesas.com>