ASoC: imx: merge sound/soc/imx into sound/soc/fsl

Freescale PowerPC and ARM/IMX families share the same SSI IP block.
The patch merges sound/soc/imx into sound/soc/fsl, so that the possible
code sharing and consolidation can happen.

This is a plain merge, except that menuconfig SND_POWERPC_SOC is added
in Kconfig for PowerPC platform as a correspondence to SND_IMX_SOC for
IMX platform.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>