pinctrl: baytrail: Serialize all register access

There is a hardware issue in Intel Baytrail where concurrent GPIO register
access might result reads of 0xffffffff and writes might get dropped
completely.

Prevent this from happening by taking the serializing lock in all places
where it is possible that more than one thread might be accessing the
hardware concurrently.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>