drm/amd/pm: Use external link order for xgmi data

xgmi_port_num interface reports external link number for port number. To
be consistent, use the external link number for reporting other XGMI
link data also.

v2: For invalid link number return -EINVAL (Kevin)

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Acked-by: Yang Wang <kevinyang.wang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>