i965/cs: Add a binding table entry for gl_NumWorkGroups

i965/cs: Add a binding table entry for gl_NumWorkGroups

If glDispatchComputeIndirect is used, then the value for this variable
must be read from the indirect BO.

To allow the same generated code to support indirect and
glDispatchCompute, we will also setup a BO for the number of work
groups using the intel_upload_data mechanism. This will only be
required if the gl_NumWorkGroups variable is accessed.

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