mfd: Convert WM8350 to genirq

This gives us use of the diagnostic facilities genirq provides and
will allow implementation of interrupt support for the WM8350 GPIOs.
Stub functions are provided to ease the transition of the individual
drivers, probably after additional work to pass the IRQ numbers via
the struct devices.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>