When requesting a gpio as an interrupt, we should make sure to mux the
pin as the GPIO function and configure it to be an input so that various
functions or output signals don't affect the interrupt state of the pin.
So far, we've relied on pinmux configurations in DT to handle this, but
let's explicitly configure this in the code so that DT implementers
don't have to get this part right.

Cc: Doug Anderson <dianders@chromium.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>