When SurfaceFlinger -- or any BufferQueue consumer -- releases a buffer, the
BufferQueue calls back into the producer side in case the producer cares.
This results in a notification from surfaceflinger to bootanim.

This callback started in d1c103655533321b5c74fbefff656838a8196153.

Addresses the following denial:

6.164348   type=1400 audit(1397612702.010:5): avc:  denied  { call } for  pid=128 comm="surfaceflinger" scontext=u:r:surfaceflinger:s0 tcontext=u:r:bootanim:s0 tclass=binder

Change-Id: I6f2d62a3ed81fde45150d2ae3ff05822bfda33fe