arm64: dts: qcom: sm8250: add pinctrl for SPI using GPIO as a CS

GENI SPI controller shows several issues if it manages the CS on its own
(see 37dd4b77 ("arm64: dts: qcom: sc7180: Provide pinconf for SPI to
use GPIO for CS")) for the details. Provide pinctrl entries for SPI
controllers using the same CS pin but in GPIO mode.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>