drm/amd/display: Set FEC_READY always before link training

[why]
Right now we FEC_READY is set only before the final link training,
i.e. at mode set time. This means FEC_READY won't be set when doing
link training as a response to HPD. It also fails UCD400 FEC test in
DP compliance.

[how]
Move FEC_READY setup to link training.

Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Abdoulaye Berthe <Abdoulaye.Berthe@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>