nir: add bit_size parameter to system values with multiple allowed bit sizes

v2: add assert to verify we have at least one valid bit_size
v3: fix use of load_front_face in nir_lower_two_sided_color and tgsi_to_nir

Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>

src/compiler/nir/nir_lower_system_values.c

@@ -261,8 +261,8 @@ convert_block(nir_block *block, nir_builder *b)
       if (sysval == NULL) {
          nir_intrinsic_op sysval_op =
             nir_intrinsic_from_system_value(var->data.location);
-         sysval = nir_load_system_value(b, sysval_op, 0);
-         sysval->bit_size = load_deref->dest.ssa.bit_size;
+         sysval = nir_load_system_value(b, sysval_op, 0,
+                                        load_deref->dest.ssa.bit_size);
       }
 
       nir_ssa_def_rewrite_uses(&load_deref->dest.ssa, nir_src_for_ssa(sysval));