Previously, any uses of global motion inside supertx blocks were not
counted correctly. This caused encode/decode mismatches when every use
of global motion in a frame occurred inside supertx blocks.
This happened in, for example, AV1/ActiveMapTest.Test/0

This patch makes update_state_supertx count global motion usages in
the same way update_state does, and fixes the above problem.

Change-Id: Id500d5a24c565774fa3aa3b52cd3fdbeab75b486