ASoC: fsl_ssi: Add dual fifo mode support

By enabling dual fifo mode, it would allow SSI enter a better performance
to transimit/receive data without occasional hardware underrun/overrun.

Signed-off-by: Nicolin Chen <b42378@freescale.com>
Acked-by: Timur Tabi <timur@tabi.org>
Acked-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>