libstagefright: Return EOS after buffers are released

Return EOS from SurfaceMediaSource after buffers
have been released, due to disconnect from producer..

CRs-Fixed: 550868
Change-Id: I4b2f3ef1c2895f155260baa0c58d90df4b4210d9
libstagefright: adjust AV sync late margin based on property

- Current AV late margin is 40 ms
- Read system property media.sf.set.late.margin and if
  new AV sync late margin is set then use the same
- Max AV sync late margin allowed is 250 ms
- Min AV sync late margin is default 40 ms

Change-Id: I65cd3dce9b31b87f1488c37af9618669b29c362c