drm/amd/display: Add option to disable PHY SSC reduction on transmitter enable

[WHY]
On some 8k display models flickering or black screens may occur at reduced
PHY SSC.

[HOW]
Add an option to set a workaround bit for these displays to keep the old
SSC value.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Muhammad Ahmed <Muhammad.Ahmed@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>