mfd: Add WM8350 interrupt support

The WM8350 has an interrupt line to the CPU which is shared by the
devices on the CPU. This patch adds support for the interrupt
controller within the WM8350 which identifies which identifies the
interrupt cause. In common with other similar chips this is done
outside the standard interrupt framework due to the need to access
the interrupt controller over an interrupt-driven bus.

This code was all originally written by Liam Girdwood with updates for
submission by me.

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