pinctrl: merrifield: Convert to use new memeber in struct intel_function

Convert driver to use generic data type and hence a new member in
the struct intel_function. No functional change intended.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>