arm64: dts: qcom: qrb5165-rb5: switch into using GPIO for SPI0 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. Configure SPI0 CS pin as a GPIO.

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