mfd: twl4030-audio: Rearange and clean-up the probe function

To facilitate the device tree support the probe function need to be rearanged.
Small cleanup in the APLL frequency selection part as well.

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>