mfd: arizona: Core driver

Several forthcoming Wolfson devices are based on a common platform
known as Arizona allowing a great deal of reuse of driver code. This
patch adds core support for these devices.

In order to handle systems which do not use the generic clock API a
simple wrapper for the 32kHz clock domain in the devices is provided.
Once the generic clock API is widely available this code will be moved
over to use that.

For simplicity some WM5102 specific code is included in the core driver,
the effort involved in splitting the device out isn't worth it.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>