broadcom/vc5: Set the snorm/unorm packing functions to be lowered.

We don't have native instructions for them, so set up the lowering.  Once
we support the bfi instructions that get generated, they should start
actually working.

src/broadcom/compiler/nir_to_vir.c

@@ -1982,6 +1982,10 @@ const nir_shader_compiler_options v3d_nir_options = {
         .lower_extract_word = true,
         .lower_bitfield_insert = true,
         .lower_bitfield_extract = true,
+        .lower_pack_unorm_2x16 = true,
+        .lower_pack_snorm_2x16 = true,
+        .lower_pack_unorm_4x8 = true,
+        .lower_pack_snorm_4x8 = true,
         .lower_ffma = true,
         .lower_flrp32 = true,
         .lower_fpow = true,