spi: spi-mem: fallback to using transfers when CS gpios are used

Devices with chip selects driven via GPIO are not compatible with the
spi-mem operations. Fallback to using standard spi transfers when the
device is connected with a gpio CS.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Link: https://lore.kernel.org/r/20191107044235.4864-3-chris.packham@alliedtelesis.co.nz


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