pinctrl: qcom: handle input-enable pinconf property

This enables support of 'input-enable' pinconf generic property in
the pinctrl driver.

Signed-off-by: Stanimir Varbanov <svarbanov@mm-sol.com>
Acked-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>