pinctrl: Introduce pinctrl driver for Qualcomm pm8xxx

This introduces a pinctrl, pinconf, pinmux and gpio driver for the gpio
block found in pm8018, pm8038, pm8058, pm8917 and pm8921 pmics from
Qualcomm.

Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>