regulator: Add WM8350 regulator support

The WM8350 features six DCDC convertors (four buck and two boost), four
LDO voltage regulators and two constant current sinks. This driver adds
support for these through the regulator API.

This driver was written by Liam Girdwood with updates for submission
from Mark Brown.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>