spi: spi-mem: Add Realtek SPI-NAND controller

Add a driver for the SPI-NAND controller on the RTL9300 family of
devices.

The controller supports
* Serial/Dual/Quad data with
* PIO and DMA data read/write operation
* Configurable flash access timing

There is a separate ECC controller on the RTL9300 which isn't currently
supported (instead we rely on the on-die ECC supported by most SPI-NAND
chips).

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Link: https://patch.msgid.link/20241015225434.3970360-4-chris.packham@alliedtelesis.co.nz


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