spi: dt-bindings: renesas,rzv2h-rspi: document RZ/T2H and RZ/N2H

spi: dt-bindings: renesas,rzv2h-rspi: document RZ/T2H and RZ/N2H

The Renesas RZ/T2H (R9A09G077) and RZ/N2H (R9A09G087) SoCs have four SPI
peripherals.

Compared to the previously supported RZ/V2H, these SoCs have a smaller
FIFO, no resets, and only two clocks: PCLKSPIn and PCLK. PCLKSPIn,
being the clock from which the SPI transfer clock is generated, is the
equivalent of the TCLK from V2H.

Document them, and use RZ/T2H as a fallback for RZ/N2H as the SPIs are
entirely compatible.

Signed-off-by: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@renesas.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20251119161434.595677-11-cosmin-gabriel.tanislav.xa@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>