iris: Avoid uploading SURFACE_STATE descriptors for UBOs if possible

iris: Avoid uploading SURFACE_STATE descriptors for UBOs if possible

If we can entirely push uniform data, we don't need a SURFACE_STATE
descriptor for pulling data.  Since constant uploads are a very common
operation, and being able to push all data is also very common, we would
like to avoid the overhead in this case.

This patch defers uploading new descriptors.  Instead of handling that
at iris_set_constant_buffer, we do it at iris_update_compiled_shaders,
where we can see the currently bound shader variants.  If any need pull
descriptors, and descriptors are missing, we update them and flag that
the binding table also needs to be refreshed.

Improves performance in GFXBench5 gl_driver2 on an i7-6770HQ by
31.9774% +/- 1.12947% (n=15).

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>