drm/amdgpu: check ASPM on the dGPU host link

drm/amdgpu: check ASPM on the dGPU host link

dGPUs with an internal PCIe switch expose graphics functions below the
switch downstream port. The automatic ASPM check uses the display
endpoint and evaluates the internal link instead of the host link.

Use the switch upstream port for the check and report the selected
link.

Fixes: 0ab5d711ec74 ("drm/amd: Refactor `amdgpu_aspm` to be evaluated per device")
Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 4e0d6f2876e704fff707b18c40dbd383aea4a1c9)
Cc: stable@vger.kernel.org