!UPSTREAM: i965/gs: Make EndPrimitive() work with >32 vertices

TODO:
- Move to appropriate place in series
!UPSTREAM: i965/gen7: Add the ability to send URB_WRITE_OWORD messages.

This will be used by geometry shaders to implement EndPrimitive()
functionality.

TODO:
- Move to appropriate place in series.
squash! i965/gen7: Allow URB_WRITE_HWORD channel masks to be used.

Don't talk about HWORD anymore.