ASoC: tlv320dac33: Some cleanup for 32/24 bit support

Change the structure of FIFO handling in order to
pave the way for adding 32/24 bit audio support.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>