drm/amd/display: check hpd before retry verify link cap

[why]
During detection link training if a display is disconnected,
the current code will retry 3 times of link training
on disconnected link before giving up.

[how]
Before each retry check for HPD status, only retry
verify link cap when HPD is still high.
Also put a 10ms delay between each retry to improve
the chance of success.

Signed-off-by: Wenjing Liu <Wenjing.Liu@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@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>