drm/amdgpu: Change GART offset to 64-bit

drm/amdgpu: Change GART offset to 64-bit

commit cab0b8d50e9bbef62c04067072c953433a87a9ff upstream.

The GART aperture size can be bigger than 4GB. Therefore the offset
used in amdgpu_gart_bind and amdgpu_gart_unbind must be 64-bit.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>