mfd: Add WM8325 support

The WM8325 is a PMIC for low power, high performance applications.  From
a software point of view the device is identical to the WM8320, all the
differences are at the hardware level.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>