Merge tag 'cadence-mtd-spi-move' into spi-nor/next

mtd/spi: Move the cadence-quadspi driver to spi-mem

cadence-quadspi has been converted to use the SPIMEM framework,
and moved under drivers/spi/. The series was taken through the
SPI tree. Merge it also in spi-nor/next to avoid conflicts during
the release cycle.