pinctrl: Add void * to pinctrl_pin_desc

drv_data is added to the pinctrl_pin_desc for drivers to define additional
driver-specific per-pin data.

Signed-off-by: Sherman Yin <syin@broadcom.com>
Reviewed-by: Christian Daudt <bcm@fixthebug.org>
Reviewed-by: Matt Porter <matt.porter@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>