drm/amd/display: Clearly states if long or short HPD event in dmesg logs

[Why]
The log "DMUB HPD callback" is crucial to identify when DP tunneling
is been established and driver is notified of this event from DMUB.
Same log is shared for long and short hotplug event and we need to
check trailing DC debug log to distinguish between them two, making
debugging on DPIA related issues a bit more troublesome.

[How]
Clearly states in dmesg logs whether this is a long or short hotplug
event.

Reviewed-by: Hamza Mahfooz <Hamza.Mahfooz@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Stylon Wang <stylon.wang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>