ALSA: pcm - add support for hostless audio

Allow some PCM devices to be hostless, i.e. there is no
PCM data transferred to or from the host CPU. This can
be used to minimise power on system since the CPU can
idle/sleep during the PCM device operation (e.g. a phone
call where the DAI is between a MODEM and DSP).

TODO: cleanup, look at adding a read/write blocker.

Change-Id: Ib9bef6710b9af2b0a2785d81afb252a4e7ca7d4b
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Patrick Lai <plai@codeaurora.org>
Git-commit: efea68f4f76c7d921201bbb1410a370dfd5ce83c
Git-repo: https://source.codeaurora.org/quic/la/kernel/msm/log/?h=msm-2.6.38


[bgoswami@codeaurora.org: Fix checkpatch errors
 for line over 80 characters in commit text.]
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>
Signed-off-by: Meng Wang <mwang@codeaurora.org>