drm/i915: Check for FRL training before DP Link training

This patch calls functions to check FRL training requirements
for an HDMI2.1 sink, when connected through PCON.
The call is made before the DP link training. In case FRL is not
required or failure during FRL training, the TMDS mode is selected
for the pcon.

v2: moved check_frl_training() just after FEC READY, before
starting DP link training.

v3: rebase

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201218103723.30844-11-ankit.k.nautiyal@intel.com