drm/amd/display: ensure FS is enabled before sending request to DMUB for FS changes

[Why]
ignore_msa_timing_param indicates FS is capable but not necessarily enabled

[How]
add check for either allow_freesync or vrr_active_variable to confirm FS is enabled

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Samson Tam <samson.tam@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>