i965/gs: Add the gl_prim_to_hw_prim table to vec4_gs_visitor.cpp

i965/gs: Add the gl_prim_to_hw_prim table to vec4_gs_visitor.cpp

It's currently in brw_util.c but that's the only bit of brw_util.c
that's shared between the compiler and the rest of the GL driver.
It's just a fairly obvious table so the duplication isn't bad.  It's
certainly less pain than trying to figure out how to share the code.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>