[WHY]
Freesync borderless is not meant to be enabled on any APUs

[HOW]
Add is_apu cap to dcn21_resource_construct for correct recognition
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>