mfd: twl4030-audio: Add DT support

Support for loading the twl4030 audio module via devicetree.
Sub devices for codec and vibra will be created as mfd devices once the
core MFD driver is loaded when the kernel is booted with a DT blob.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>