drm/i915/dp: Reset frl trained flag before restarting FRL training

drm/i915/dp: Reset frl trained flag before restarting FRL training

For cases where DP has HDMI2.1 sink and FRL Link issues are detected,
reset the flag to state FRL trained status before restarting FRL
training.

Fixes: 9488a030ac91 ("drm/i915: Add support for enabling link status and recovery")
Cc: Swati Sharma <swati2.sharma@intel.com>
Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Cc: Uma Shankar <uma.shankar@intel.com> (v2)
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221011063447.904649-2-ankit.k.nautiyal@intel.com
(cherry picked from commit 47e1a59e60c688c5f95b67277202f05b7e84c189)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>