nir: Add helpers for working with deref instructions

This commit adds a pass for lowering deref instructions to deref chains
as well as some smaller helpers to ease the transition.

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/meson.build

@@ -92,6 +92,7 @@ files_libnir = files(
   'nir_control_flow.c',
   'nir_control_flow.h',
   'nir_control_flow_private.h',
+  'nir_deref.c',
   'nir_dominance.c',
   'nir_format_convert.h',
   'nir_from_ssa.c',