drm/amd/display: Adding interface to log hw state when underflow happens

[why]
Will help us better debug underflow issues.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Muhammad Ahmed <Muhammad.Ahmed@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>