ASoC: mxs-saif: Remove platform data

All MXS users have been converted to device tree and the board files have been
removed.

No need to keep platform data in the driver.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Dong Aisheng <dong.aisheng@linaro.org>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>