pinctrl: add pinctrl/GPIO driver for Apple SoCs

This driver adds support for the pinctrl / GPIO hardware found
on some Apple SoCs.

Co-developed-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Stan Skowronek <stan@corellium.com>