[WHY & HOW]
1) We did linear/non linear transition properly long ago
2) We used that path to handle SystemDisplayEnable
3) We fixed a SystemDisplayEnable inability to fallback to passive by
   impacting the transition flow generically
4) AFMF later relied on the generic transition behavior

Separating the two flows to make (3) non-generic is the best immediate
coarse of action.

DC can discern SSAMPO3 very easily from SDE.

Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Chris Park <chris.park@amd.com>
Signed-off-by: Charlene Liu <Charlene.Liu@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>