libstagefright: Fix for failure in LPA clip playback

-When non-LPA clip follows an LPA clip in Music App,
 playback of LPA clip fails.
-setNextPlayer causes the loading of decoder omx component
 and acquires the DSP resources for non-LPA clip, even before
 LPA clip acquires DSP resources.
-Move mp3 and aac to sw decoders.

Change-Id: Ie04e8ffe5a5822245301a52b3fc8613fb1dab1ef