drm/amd/display: fix memory leak in resource pools

drm/amd/display: fix memory leak in resource pools

[why]
ddc engines were recently changed to be independently tracked
from pipe count.  the change was reflected in resource constructor
but not in destructor.  this manifests as a memory leak when
pipe harvesting is enabled, since not all constructed ddc engines
are freed

[how]
make destructor symmetric with constructor for all dcX_resource

Signed-off-by: Jun Lei <Jun.Lei@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>