GENI SPI controller shows several issues if it manages the CS on its own
(see 37dd4b777942 ("arm64: dts: qcom: sc7180: Provide pinconf for SPI to
use GPIO for CS") for the details). Configure SPI0 CS pin as a GPIO.
Changes since v1:
- Split sm8250's spi pin config into mux/config parts, split away CS
handling from main SPI pinctrl nodes.
