Allows us to use the 3D engine for memory management
and allows us to use vram beyond the BAR aperture.

v2: fix copy paste typo
Reported-by: NNils Wallménius <nils.wallmenius@gmail.com>
Signed-off-by: NAlex Deucher <alexdeucher@gmail.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>