drm/amd/display: Retrieve windowed fullscreen state

- Retrieve windowed fullscreen state when getting freesync params.

Signed-off-by: Andrew Wong <andrew.wong1@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>