pinctrl: qcom: add infrastructure for marking pin functions as GPIOs

Add a helper macro that wraps PINCTRL_GPIO_PINFUNCTION() for pinctrl-msm
pin functions and assign the .function_is_gpio() callback in pinmux_ops.

Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Tested-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>