gpio: merrifield: Add support of ACPI enabled platforms

The driver needs the pin control device name for ACPI.

We are looking through ACPI namespace and return first found device
based on ACPI HID for Intel Merrifield FLIS (pin control device).

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>