Additions/x11/vboxvideo: Drop dependency on IPRT header files.
bugref:9017: Additions/x11: put vboxvideo into upstream X.Org
Remove (hopefully) all dependencies on IPRT header files inside of the X.Org
vboxvideo driver and provide the dependencies which are still useful in the
form of a single, local VBoxVideoIPRT.h file. These are mainly definitions
and macros.
