Stats/PreEnc: Add basic infrastructure for PreEnc enablement

Stats/PreEnc: Add basic infrastructure for PreEnc enablement

Add necessary changes in common structures and apis
to support Stats Entrypoint.

* add support for the new entrypoint VAEntrypointStats
* added new preproc encode operation enum
* define virtual methods for preproc_set_curbe/send_surface
* add fixes in vaQueryConfigEntrypoints(), vaQueryConfigProfiles,
  vaGetConfigAttributes(), vaQuerySurfaceAttributes(),
  vaCreateContext(), vaCreateBuffer(),vaBeginPicture(),
  vaRenderPicture() and vaEndPicture()
* If PreEnc enabled, only invoke VME.

Note: Enabled the PreEnc Support only for avc encode in Skylake.

libva PR: https://github.com/01org/libva/pull/110

Signed-off-by: Sreerenj Balachandran <sreerenj.balachandran@intel.com>