ASoC: sti-sas: Add sti platform codec

Codec part of the sti platform that supports codec IPs.
This first version does not support HDMI, but only DAC and SPDIF out.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>