drm/amd/display: Revert DP2 MST hub triple display fix

[WHY]
Introduces regression with DP2 native displays

[HOW]
Revert the change

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>