ARM: dts: renesas: Clean up R8A779G0 V4H RPC SPI DT node

Use the phandle reference to &rpc node in arch/arm/dts/r8a779g0.dtsi
and remove properties which are already in arch/arm/dts/r8a779g0.dtsi.
No functional change and no resulting DT change.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>