drm/amdgpu:PTE flag should be 64 bit width

otherwise we'll lost the high 32 bit for pte, which lead
to incorrect MTYPE for vega10.

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>