radv: don't expose linear depth surfaces on SI/CIK/VI either.

radv: don't expose linear depth surfaces on SI/CIK/VI either.

ac_surface.c: gfx6_compute_surface says
/* DB doesn't support linear layouts. */

Now if we expose linear depth and create a linear depth image
and use CmdCopyImage to copy into it, we can't map the underlying
memory and read it linearly which I think should work.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>