drm/amd/pm: bug fix for pcie dpm

Currently the pcie dpm has two problems.
1. Only the high dpm level speed/width can be overrided
if the requested values are out of the pcie capability.
2. The high dpm level is always overrided though sometimes
it's not necesarry.

Signed-off-by: Kenneth Feng <kenneth.feng@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org