Add RecordThread media.log and deferred deallocation

This change allows a media.log buffer for RecordThread.

Unlike playback threads which stick around forever, the RecordThread comes
and goes for every capture session.  This means that the media.log buffer
for a RecordThread would disappear too, and so was useless.  Now when a
thread exits, it's associated media.log buffer is just marked for deferred
deallocation.  It is only actually freed when the memory is needed.

Other changes:
 - Fix bug in unregistering comparison, it was comparing the wrong pointers
 - Increased size of log area so we can log for RecordThread also

Change-Id: If45d4c03a793b86390a0112ec3acc5d41b2e3635