nir: Add a pass for lowering away constant initializers

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>

src/compiler/nir/nir.h

@@ -2340,6 +2340,8 @@ void nir_lower_io_types(nir_shader *shader);
 void nir_lower_vars_to_ssa(nir_shader *shader);
 
 bool nir_remove_dead_variables(nir_shader *shader, nir_variable_mode modes);
+bool nir_lower_constant_initializers(nir_shader *shader,
+                                     nir_variable_mode modes);
 
 void nir_move_vec_src_uses_to_dest(nir_shader *shader);
 bool nir_lower_vec_to_movs(nir_shader *shader);