ASoC: mmp: add sspa support

The SSPA is a configurable multi-channel audio serial (TDM) interface.
It's configurable at runtime to support up to 128 channels and the
number of bits per sample: 8, 12, 16, 20, 24 and 32 bits. It also
support stereo format: I2S, left-justified or right-justified.

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>