drm/amd/display: minor dp link training refactor

[how]
The change includes some dp link training refactors:
1. break down is_ch_eq_done to checking individual conditions in
its own function.
2. update dpcd_set_training_pattern to take in dc_dp_training_pattern
as input.
3. moving lttpr mode struct definition into link_service_types.h

Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Reviewed-by: George Shen <George.Shen@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>