mach-snapdragon: Introduce pinctrl driver

This patch adds pinmux and pinctrl driver for TLMM
subsystem in snapdragon chipsets.
Currently, supporting only 8016, but implementation is
generic and 8096 can be added easily.

Driver is using the generic dt-bindings and doesn't
introduce any new bindings (yet).

Signed-off-by: Ramon Fried <ramon.fried@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>