power_supply: Add support for WM8350 PMU

This patch adds support for the PMU provided by the WM8350 which
implements battery, line and USB supplies including a battery charger.
The hardware functions largely autonomously, with minimal software
control required to initiate fast charging.

Support for configuration of the USB supply is not yet implemented.
This means that the hardware will remain in the mode configured at
startup, by default limiting the current drawn from USB to 100mA.

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

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Anton Vorontsov <cbouatmailru@gmail.com>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>