ASoC: fsl: remove use of imx-pcm-audio from imx-ssi

Rather than instantiating imx-pcm-audio to call imx_pcm_dma_init(),
imx-ssi can just directly call it to save the use of imx-pcm-audio.
With this change, imx-ssi becomes not only a cpu DAI but also a
platform device, so updates platform device setup in imx-mc13783 and
mx27vis-aic32x4 accordingly.

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