This will only be setup when the prog_data uses_num_work_groups
boolean is set.

At this point nothing will set uses_num_work_groups, but soon code
will set it when emitting code for the intrinsic that loads
gl_NumWorkGroups.

We can't emit this surface information earlier at the start of the
DispatchCompute* call because we may not have generated the program
yet. Until we generate the program, we don't know if the
gl_NumWorkGroups variable is accessed.

We also can't emit the surface as part of the brw_cs_state atom,
because we might not need the surface if gl_NumWorkGroups is not used
by the program.

Lastly, we cannot emit the surface later (after state upload) in the
DispatchCompute* call, because it needs to be run before the
brw_cs_state atom is emitted, since it changes the surface state.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>