pinctrl: intel: Add Intel Merrifield pin controller support

This driver adds pinctrl support for Intel Merrifield. The IP block which is
called Family-Level Interface Shim is a separate entity in SoC. The GPIO driver
(gpio-intel-mid.c) will be updated accordingly to support pinctrl interface.

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