ASoC: sti-asoc-card: update tdm mode

- Add "TDM" in the st,mode property list
- st,mode property is also mandatory for reader
- add tdm playback dai-link example

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