radv: don't lower_pack() after load-store-vectorization

radv: don't lower_pack() after load-store-vectorization

Totals from 7 (0.01% of 139391) affected shaders:
CodeSize: 282900 -> 283324 (+0.15%); split: -0.01%, +0.16%
Instrs: 45287 -> 45338 (+0.11%); split: -0.01%, +0.12%
Cycles: 11496332 -> 11510396 (+0.12%); split: -0.00%, +0.12%
VMEM: 2355 -> 2335 (-0.85%)
Copies: 15506 -> 15561 (+0.35%)

A bit of noise in some parallel-rdp shaders.

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8425>