Add an OMX IL API for querying buffer usage flags.

This change defines an OpenMAX IL API for querying from the IL component
the gralloc buffer usage flags that should be used to allocate the
buffers.  It also adds the Stagefright plumbing for using the new OMX IL
API.

Change-Id: I046b5e7be70ce61e2a921dcdc6e3aa9324d19ea6
Related-Bug: 3479027