spi: Add driver for the RZ/V2H(P) RSPI IP

The Renesas RZ/V2H(P) RSPI IP supports 4-wire and 3-wire
serial communications in both host role and target role.
It can use a DMA, but the I/O can also be driven by the
processor.

RX-only, TX-only, and RX-TX operations are available in
DMA mode, while in processor I/O mode it only RX-TX
operations are supported.

Add a driver to support 4-wire serial communications as
host role in processor I/O mode.

Signed-off-by: Fabrizio Castro <fabrizio.castro.jz@renesas.com>

Link: https://patch.msgid.link/20250704162036.468765-3-fabrizio.castro.jz@renesas.com


Signed-off-by: Mark Brown <broonie@kernel.org>