ASoC: fsl: remove imx-pcm driver

With imx-pcm-dma moving to generic dmaengine pcm driver and the removal
of imx-pcm-audio/imx-fiq-pcm-audio platform device use, now imx-pcm
driver contains a few functions that are only used by imx-pcm-fiq.c.
Move these functions into imx-pcm-fiq.c and remove imx-pcm.c completely.

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