ARM: dts: renesas: Minimize R8A779G0 V4H RPC SPI DT node

ARM: dts: renesas: Minimize R8A779G0 V4H RPC SPI DT node

The RPC SPI DT node is now part of mainline Linux DT, remove the
duplicate content from U-Boot DT extras. The SPI flash DT node name
has been changed from "spi-flash@0" to "flash@0", reflect this change
in this patch. Retain "bank-width" and "num-cs" DT properties which
are used by U-Boot. Retain "spi-rx-bus-width" and "spi-tx-bus-width"
DT properties to indicate the bus should always be operated in 1-1-1
mode as the U-Boot RPC SPI driver does not support higher bus width
modes yet.

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