regulator: Add WM831x LDO support

The WM831x series of devices provide three types of LDO:

 - General purpose LDOs supporting voltages from 0.9-3.3V
 - High performance analogue LDOs supporting voltages from 1-3.5V
 - Very low power consumption LDOs intended to support always on
   functionality.

This patch adds support for all three kinds of LDO. Each regulator
is probed as an individual platform device with resources used to
provide the register map location of the regulator. Mixed hardware
and software control of regulators is not current supported.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>