Binder: allow stability downgrade

For instance, use a VINTF interface inside the system image without
adding it to the VINTF manifest (e.g. for testing, in this case, the
interface can't be used between system and vendor).

Bug: 183154648
Test: N/A
Change-Id: I9ceb5d96e6a245b9509d9c60828aa3736056909d