intel/brw: Replace some fs_reg constructors with functions

Create three helper functions for ATTR, UNIFORM and VGRF creation.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29791>

src/intel/compiler/brw_fs_thread_payload.cpp

@@ -399,7 +399,7 @@ cs_thread_payload::load_subgroup_id(const fs_builder &bld,
       assert(gl_shader_stage_is_compute(bld.shader->stage));
       int index = brw_get_subgroup_id_param_index(devinfo,
                                                   bld.shader->prog_data);
-      bld.MOV(dest, fs_reg(UNIFORM, index, BRW_TYPE_UD));
+      bld.MOV(dest, brw_uniform_reg(index, BRW_TYPE_UD));
    }
 }