drm/amdgpu: add TOPDOWN flag to the whole vram

need to decrease visible vram usage by default.

Signed-off-by: Chunming Zhou <[e-mail]>
Reviewed-by: monk.liu <[e-mail]>
Reviewed-by: Christian König <[e-mail]>

drivers/gpu/drm/amd/amdgpu/amdgpu_object.c

···
 		placements[c].fpfn = 0;
 		placements[c++].flags = TTM_PL_FLAG_WC | TTM_PL_FLAG_UNCACHED |
 			TTM_PL_FLAG_VRAM;
+		if (!(flags & AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED))
+			placements[c - 1].flags |= TTM_PL_FLAG_TOPDOWN;
 	}
 
 	if (domain & AMDGPU_GEM_DOMAIN_GTT) {