dt-bindings: pinctrl: qcom: Add sm8250 pinctrl bindings

Add device tree binding Documentation details for Qualcomm SM8250
pinctrl driver.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20200417061907.1226490-2-bjorn.andersson@linaro.org


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>