drm/amd/display: optionally optimize edp link rate based on timing

[Why]
eDP v1.4 allows panels to report link rates other than RBR/HBR/HBR2, that
may be more optimal for the panel's timing. Power can be saved by using
a link rate closer to the required bandwidth of the panel's timing.

[How]
Scan the table of reported link rates from the panel, and select the
minimum link rate that satisfies the bandwidth requirements of the panel's
timing. Include a flag to make the feature optional.

Signed-off-by: Josip Pavic <Josip.Pavic@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>