drm/amd/display: Separate fec debug flag and monitor patch

[Why]
Driver apply the monitor patch into global debug flag.  When apply
monitor patch, fec feature will always disable.

[How]
Separate fec debug flag and monitor patch

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Lewis Huang <Lewis.Huang@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>