nir: Add a pass for fixing deref modes

This will be needed by anything which changes variable modes without
rewriting derefs.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Acked-by: Rob Clark <robdclark@gmail.com>
Acked-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Acked-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/compiler/nir/nir.h

@@ -2701,6 +2701,8 @@ bool nir_lower_deref_instrs(nir_shader *shader,
 void nir_lower_var_copy_instr(nir_intrinsic_instr *copy, nir_shader *shader);
 bool nir_lower_var_copies(nir_shader *shader);
 
+void nir_fixup_deref_modes(nir_shader *shader);
+
 bool nir_lower_global_vars_to_local(nir_shader *shader);
 
 bool nir_lower_indirect_derefs(nir_shader *shader, nir_variable_mode modes);