drm/i915/dp: Queue a link check after link training is complete

After link training - both in case of a passing and failing LT result -
a work is scheduled to check the link state. This check should take
place after the link training is completed by disabling the link
training pattern and setting intel_dp::link_trained=true. Atm, the work
is scheduled before these steps, which may result in checking the link
state too early (and thus not retraining the link as expected).

Fix the above by scheduling the link check work after link training is
complete.

v2:
- Add MAX_SEQ_TRAIN_FAILURES instead of open-coding it. (Jani)

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250305114820.3523077-2-imre.deak@intel.com