spi: rockchip: Support cs-gpio

1.Add standard cs-gpio support
2.Refer to spi-controller.yaml for details

Signed-off-by: Jon Lin <jon.lin@rock-chips.com>
Link: https://lore.kernel.org/r/20210621104848.19539-1-jon.lin@rock-chips.com


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