arm64: dts: renesas: r8a779a0: Add RPC node

Add device node for RPC on R8A779A0 SoC.

Signed-off-by: Duc Nguyen <duc.nguyen.ub@renesas.com>
[wsa: rebased]
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20211006085836.42155-4-wsa+renesas@sang-engineering.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>