ASoC: fsl: Add S/PDIF CPU DAI driver

This patch implements a device-tree-only CPU DAI driver for Freescale
S/PDIF controller that supports stereo playback and record feature.

Signed-off-by: Nicolin Chen <b42378@freescale.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@linaro.org>