drm/amd/display: Add debug flags for USB4 DP link training.

drm/amd/display: Add debug flags for USB4 DP link training.

[Why & How]
Additional debug flags that can be useful for testing USB4 DP
link training.

Add flags:
- 0x2 : Forces USB4 DP link to non-LTTPR mode
- 0x4 : Extends status read intervals to about 60s.

Reviewed-by: Meenakshikumar Somasundaram <meenakshikumar.somasundaram@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Wayne Lin <Wayne.Lin@amd.com>
Acked-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Jimmy Kizito <Jimmy.Kizito@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>