radv/gfx9: add support for 3d images to blit 2d paths

This add support for a 3D image reading path to the blit 2d paths,
like I did for the clear paths.

Fixes: e38685cc 'Revert "radv: disable support for VEGA for now."'
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Tested-by: Alex Smith <asmith@feralinteractive.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
(cherry picked from commit 9f675bf9)