drm/amd/display: reset lane settings after each PHY repeater LT

drm/amd/display: reset lane settings after each PHY repeater LT

[why]
In LTTPR non-transparent mode, we need
to reset the cached lane settings before performing
link training on the next PHY repeater. Otherwise,
the cached lane settings will be used for the next
clock recovery e.g. VS = MAX (3) which should not be
the case according to the DP specs. We expect to use
minimum lane settings on each clock recovery sequence.

[how]
Reset DPCD and HW lane settings on each repeater LT.
Set training pattern to 0 for the repeater that failed LT
at the proper place.

Reviewed-by: Meenakshikumar Somasundaram <Meenakshikumar.Somasundaram@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Sung Joon Kim <sungkim@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>