OMAP3: McBSP: Add interface for FIFO caused delay query

New functions for querying the FIFO caused delay on both
TX and RX path.
On TX path the return value shows the number of used
locations in the FIFO.
On RX papth it returns the number of locations to be filled
to reach the threshold value (DMA will be triggered to read
the data out from the FIFO).

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Jarkko Nikula <jhnikula@gmail.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>