ASoC: fsl: add imx-sgtl5000 machine driver

This is the initial imx-sgtl5000 machine driver support with only
playback dai link implemented.  More features can be added on top
of it later.

It's a device tree only machine driver working with fsl_ssi driver.

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>