mtd: spi-nor: cadence-quadspi: Add DMA support for direct mode reads

Add support to use DMA over memory mapped reads in direct mode. This
helps in reducing CPU usage from ~100% to ~10% when reading data from
flash. For non-DMA'able/vmalloc'd buffers, driver just falls back to CPU
based memcpy.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>