nak: Set lower_pack_64_4x16

Otherwise, these can cause infinite loops in optimization because there
aren't _split variants and the optimizer tries to combine and split
things infinitely.

Reviewed-by: Mel Henning <drawoc@darkrefraction.com>
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34849>
(cherry picked from commit efd1cddbe90f4af26716adfb6a6cc12eca1d71b3)

.pick_status.json

@@ -44,7 +44,7 @@
         "description": "nak: Set lower_pack_64_4x16",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null,
         "notes": null

src/nouveau/compiler/nak/api.rs

@@ -120,6 +120,7 @@ fn nir_options(dev: &nv_device_info) -> nir_shader_compiler_options {
     op.lower_fsqrt = dev.sm < 52;
     op.lower_bitfield_extract = dev.sm >= 70;
     op.lower_bitfield_insert = true;
+    op.lower_pack_64_4x16 = true;
     op.lower_pack_half_2x16 = true;
     op.lower_pack_unorm_2x16 = true;
     op.lower_pack_snorm_2x16 = true;