drm/amd/display: set allow_freesync parameter in DM

[Why&how]
There are cases where VRR is possible but not enabled. If allow_freesync
parameter is not set, SubVP logic defaults to checking only the ignore MSA
parameter that is always set if display is DRR capable, which breaks the system
while trying to enable SubVP on multi monitor configs where freesync
does not work due to Xorg limitation.

SubVP uses allow_freesync parameter to check if SubVP + DRR case can be executed.

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>