drm/amd/display: Add log for LTTPR

[Why & How]
Adding log for LTTPR to facilitate debugging.

Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Leo Chen <sancchen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>