ASoC: msm: Add support to have FM playback through ASM loopback mode

- Add support to provide PP on FM playback.
- Add PCM platform driver which enables ASM loopback mode
Define MultiMedia6 front-end dai

Change-Id: Ibf9d2645e706f9a3027dd356223a2135224a0337
Signed-off-by: Damir Didjusto <damird@codeaurora.org>