drm/amd/display: Set fec register init value

[Why]
We don't include this eDP FEC init on fastboot.

[How]
Set the fec to init value when stopping driver &get the fec register value to check should enable FEC.

Co-authored-by: Jingwen Zhu <Jingwen.Zhu@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Jingwen Zhu <Jingwen.Zhu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>