Fix/cleaup the conditioning for usage of the reuse-lowres
partition feature.

Replace the non-reference condition with the top temporal
layer, and put this condition in the speed feature.

This prevents doing update_partition_svc() on every
VGA frame, instead it will now only do update for VGA in
the top temporal layer frames.

Also this makes it easier to test/enable this feature
for lower layer temporal frames.

Change-Id: Ia897afbc6fe5c84c5693e310bcaa6a87ce017be5