drm/amd/display: properly configure DCFCLK when enable/disable Freesync

[Why]
Bandwidth validation is using Freesync parameters
from previous Freesync state.
Bandwidth validation ignores DCFCLK calculated
after Freesync parameters are configured

[How]
Set Freesync bandwidth parameters to its default
state before running bandwidth validation.
Take DCFCLK calculated after Freesync bandwidth
parameters are assigned and bandwidth is
recalculated.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Martin Leung <Martin.Leung@amd.com>
Reviewed-by: Nevenko Stupar <Nevenko.Stupar@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Vladimir Stempen <vladimir.stempen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>