Revert "columbia: Build bl31.bin for the 8mm as well as the 8mq"

This reverts commit d5fc6055e49a9951a3301e71639d876eb3158ef6.

Reason for revert: broke the build for enterprise, since it's still running the old tree. Will revisit later.

Change-Id: If8b7e58946310126b68593b7398cc7c1d69a831b