nir: Store num_direct_uniforms in the nir_shader.

nir: Store num_direct_uniforms in the nir_shader.

Storing this here is pretty sketchy - I don't know if any driver other
than i965 will want to use it.  But this will make it a lot easier to
generate NIR code at link time.  We'll probably rework it anyway.

(Ian suggested making nir_assign_var_locations_scalar_direct_first
 simply modify the nir_shader's fields, rather than passing pointers
 to them.  If this stays long term, we should do that.  But Jason and
 I suspect we'll be reworking this area again in the near future.)

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>