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 <[email protected]>
Signed-off-by: Vignesh Raghavendra <[email protected]>
Reviewed-by: Tudor Ambarus <[email protected]>
Acked-by: Tudor Ambarus <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mark Brown <[email protected]>