drm/amd/display: Pass vrr mode to dcn

[WHY]
New features will require knowing the vrr mode for their enablement.

[HOW]
Pass the state via a member of dc_stream.

Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Felipe Clark <Felipe.Clark@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>