Add media/openmax as an include directory

This will obviate changing Khronos's header files.

Note that all header files in media/openmax have OMX_ prefix, so the
chance of collision is already low.

Test: Compiles
Bug: 63821829
Change-Id: I40cc92409de5091a1e2ed7c89c0012000b20f68f
1 file changed