drm/amdgpu: Always enable memory sharing within same XGMI hive

XGMI Memory sharing will be disbaled by default for security reason after
boot up, it depends on driver to enable the memory sharing

Signed-off-by: shaoyunl <shaoyun.liu@amd.com>
Acked-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>