spi: cadence-qspi: Add Renesas RZ/N1 support

Merge series from "Miquel Raynal (Schneider Electric)" <miquel.raynal@bootlin.com>:

This series adds support for the QSPI controller available on Renesas
RZ/N1S and RZ/N1D SoC. It has been tested with a custom board (see last
SPI patch for details), but has been tested by Wolfram (thank you!) on
the DB board.
Link: https://lore.kernel.org/linux-devicetree/20260116114852.52948-2-wsa+renesas@sang-engineering.com/
Adding support for this SoC required a few adaptations to the Cadence
QSPI driver which have already been merged (except one regarding clocks
handling). This series contains the remaining patches, the ones actually
adding support for the RZ/N1 flavour.