ASoC: add mmp brownstone support

Adds Alsa audio platform driver for mmp brownstone machine

Signed-off-by: Zhangfei Gao <zhangfei.gao@marvell.com>
Signed-off-by: Leo Yan <leoy@marvell.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>