arm64: dts: qcom: sm8250: split spi pinctrl config

As discussed on linux-arm-msm list, start splitting sm8250 pinctrl
settings into generic and board-specific parts. The first part to
receive such treatment is the spi, so split spi pinconf to the board
device tree.

Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20210210133458.1201066-2-dmitry.baryshkov@linaro.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>