[ARM] msm: dma: various basic dma improvements and bugfixes

San:
- Propagate DM errors to the originator of the request.
- Implement msm_dmov_stop_cmd()
- Add return value to init code
- Modify msm_dmov_stop_cmd() to support ungraceful flushing

Arve:
- Disable datamover interrupt when not in use.
  We turn off the interrrupt to allow power collapse from idle.

Signed-off-by: San Mehat <san@android.com>
Signed-off-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Brian Swetland <swetland@google.com>