ASoC: msm8974: Add support for BT SCO and BT A2DP playback

Add support for BT SCO and BT A2DP playback for 8974 target.
Backend dai links for BT SCO and RT Proxy are added as part
of this change. Update RT Proxy driver with the ION memory
map changes. Also, update afe port start to handle BT SCO
and RT Proxy ports.

Change-Id: I2eab536b9cd6a1b576a88931d6fc413fe42281a2
Signed-off-by: Phani Kumar Uppalapati <phanik@codeaurora.org>