hammerhead: 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
hammerhead: Enable new mixer for offload

Change-Id: I21620d3a2612c992dc70a783f20aa8b73e8c9073