drm/amd/display: Remove unnecessary Freesync w/a from DCN32

drm/amd/display: Remove unnecessary Freesync w/a from DCN32

[Why/How]
A workaround was previously used for certain Freesync cases that would
override the vstartup_start value from DML to position the SDP
correctly. This is no longer needed in DCN32 and above, so remove the
workaround.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: George Shen <george.shen@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>