Revert "Revert drm/amd/display: Enable Freesync Video Mode by default"

This reverts commit 4243c84a.

Enables freesync video by default, since the hang and corruption issue
on eDP panels are now fixed.

Acked-by: Stylon Wang <stylon.wang@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Reviewed-by: Rodrigo Siqueira <rjordrigo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>