pinctrl: qcom: Allow SoCs to specify a GPIO function that's not 0

There's currently a comment in the code saying function 0 is GPIO.
Instead of hardcoding it, let's add a member where an SoC can specify
it.  No known SoCs use a number other than 0, but this just makes the
code clearer.  NOTE: no SoC code needs to be updated since we can rely
on zero-initialization.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Maulik Shah <mkshah@codeaurora.org>
Tested-by: Maulik Shah <mkshah@codeaurora.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20210114191601.v7.1.I3ad184e3423d8e479bc3e86f5b393abb1704a1d1@changeid


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