Restructure the codec power code in order to be able to hit
off when the codec is not in use.

Since the audio registers are accessible while the codec is powered
down, there is no need for additional safety mechanism.
Signed-off-by: NPeter Ujfalusi <peter.ujfalusi@nokia.com>
Acked-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NLiam Girdwood <lrg@slimlogic.co.uk>