Fix missing loop count for static tracks.

StaticAudioTrackServerProxy::framesReady() previously returned
only the contiguous frames, update to return the total
available frames. This resolves short-count looping in
SoundPool for FastTracks.

Also (1) Removes the racy condition of reading two variables
and (2) Fixes buffer->mNonContig to return the correct value
and (3) Restores behavior that loop count of 1 goes back to
loopStart once during playback.

Bug: 11830751
Bug: 12070295
Bug: 17456842
Change-Id: I64906e6036bb00a1d7375b03efe6deb69d6478ca