nir: prepare for bumping up max components to 16

OpenCL knows vector of size 8 and 16.

v2: rebased on master (nir_swizzle rework)
    rework more declarations with nir_component_mask_t
    adjust print_var_decl

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

src/compiler/nir/nir_opt_constant_folding.c

@@ -41,7 +41,7 @@ struct constant_fold_state {
 static bool
 constant_fold_alu_instr(nir_alu_instr *instr, void *mem_ctx)
 {
-   nir_const_value src[4];
+   nir_const_value src[NIR_MAX_VEC_COMPONENTS];
 
    if (!instr->dest.dest.is_ssa)
       return false;