libstagefright: update OMAP3 support

* Move the OMAP_ENHANCENEMENT flag to make sure that the
  buffer is not modified futher on.
* Don't queue more than 4 buffers to the component. This
  greatly improved the video recording framerates both for
  480P and 720P.

Change-Id: Iacc983214d873099e8f6218f374717a2ae4ffcc8