drm/amd/display: Add dummy interface for tracing DCN32 SMU messages

[Why/How]
Some issues may require a trace of the previous SMU messages from DC to
understand the context and aid in debugging. Actual logging to be
implemented when needed.

Reviewed-by: Josip Pavic <josip.pavic@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: George Shen <george.shen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>