drivers: pinctrl: Add simple pinctrl driver for Qualcomm/Atheros ar933x.

This is a simple pinctrl driver, it just support uart and spi pin-mux now.

Signed-off-by: Wills Wang <wills.wang@live.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
[fixed typo in commit subject line]
Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>