drm/amd/display: Fix DP LT sequence on EQ fail

[Why]
The number of lanes wasn't being reset to maximum when reducing link
rate due to an EQ failure. This could result in having fewer lanes in
the verified link capabilities, a lower maximum link bandwidth, and
fewer modes being supported.

[How]
Reset the number of lanes to max when dropping link rate due to EQ
failure during link training.

Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Signed-off-by: Ilya <Ilya.Bakoulin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>