spi: Move cadence-quadspi driver to drivers/spi/

spi: Move cadence-quadspi driver to drivers/spi/

Now that cadence-quadspi has been converted to use spi-mem framework,
move it under drivers/spi/

Update license header to match SPI subsystem style

Signed-off-by: Ramuthevar Vadivel Murugan <vadivel.muruganx.ramuthevar@linux.intel.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Acked-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20200601070444.16923-9-vigneshr@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>