drm/amd/display: Add debugfs to control DMUB trace buffer events

[Why]
We want to have a debugfs interface to enable or disable DMCUB
trace buffer events.

[How]
Add debugfs interface to enable or disable trace buffer events.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Leo (Hanghong) Ma <hanghong.ma@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>