msm8974: Enable USB audio

* Use new QCOM USB audio path which uses the AFE proxy
* With offload

Change-Id: Id08dbfec1bffa1bc083109e8f81be6509abe1db5
msm8974: Enable deep buffer output as primary

 * Since we're not offloading audio during AV playback, it's
   better to use DEEP_BUFFER as the primary output and only
   select the FAST output when the flag is set. This saves
   power during video playback.

Change-Id: I94d4de328377e9c351bd77c5ad5b0a7ec96cbb79
msm8974: Add offload properties

 * Set fragment size (same as default)
 * Enable gapless playback with offloaded streams
 * Enable offloading for AV (but not streaming AV!)

Change-Id: I1b0f8115bc880bd89f5a0c8ed13e4b54d38e0867