QSV: API 1.8 support and related improvements

Optional feature detection now done via MFXVideoENCODE_Query. This should work better with future hardware and encoder implementations.

Optional API 1.8 features are not tested (not supported by the software implementation, and no drivers with API 1.8 support available yet).


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6041 b64f7644-9d1e-0410-96f1-a4d463321fa5