ASoC: core - add hostless DAI support

Allow DAI's to be hostless so that no PCM data is sent between DAI
and CPU. This allows for power savings as there is no DMA or CPU
interaction required.

TODO: we shouldn't need to allocate a PAGE for a dummy DMA buffer.

Change-Id: I8947f1ad2c4a7013e92e21078b35e3cad332cf6f
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Patrick Lai <plai@codeaurora.org>
Git-commit: b77e8f4fb684f8afd45d4276e3dba9edd4a0c4e0
Git-repo: https://source.codeaurora.org/quic/la/kernel/msm/log/?h=msm-2.6.38


[bgoswami@codeaurora.org: fix merge conflict by moving
 code to the right source file. Fix checkpatch errors
 for line over 80 character. Fix compilation errors.]
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>
Signed-off-by: Meng Wang <mwang@codeaurora.org>