ASoC: mxs-saif: remove function in platform_data

Add master_mode and master_id in platfrom_data since it's board
specific and board knows it.
Then we can remove the function pointer in platfrom_data to make
the driver more devicetree friendly.

Signed-off-by: Dong Aisheng <b29396@freescale.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>