radv: use 3d shader for gfx9 copies if dst is 3d

This fixes some crucible 3d miptree tests I've been working on
when executed using the compute shader path.

Fixes: d08f2678 (radv/gfx9: fix 3d image to image transfers on compute queues.)
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
(cherry picked from commit 1363a47c)