drivers: Replace GPIO_CS Kconfig with devicetree detection

Use DT_INST_SPI_DEV_HAS_CS_GPIOS() in drivers to determine if we should
utilize CS_GPIO base SPI chipselect handling.  This allows us to remove
Kconfig option for this feature.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
17 files changed