ASoC: imx: set watermarks for mx2-dma

They got accidently removed by f0fba2ad

 (ASoC: multi-component - ASoC
Multi-Component Support). Reintroduce them and get rid of the
superfluous defines because the fiq-driver has its own hardcoded values.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: stable@kernel.org