drm/amd/display: Add link rate optimization logs for ILR

[Why&How]
Add logs to verify ILR optimization behaviour on boot

Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>