spi: cadence-quadspi: Add multi-chipselect support for Intel LGM SoC

Add multiple chipselect support for Intel LGM SoCs,
currently QSPI-NOR and QSPI-NAND supported.

Signed-off-by: Ramuthevar Vadivel Murugan <vadivel.muruganx.ramuthevar@linux.intel.com>
Link: https://lore.kernel.org/r/20201124041840.31066-4-vadivel.muruganx.ramuthevar@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>