keymint: use versions for imports

This makes sure that when developers add a new version of an interface,
or when interfaces are being frozen, the runtime/buildtime situation of
clients depending on those interfaces remains the same. This is required
for AIDL to continue working at scale.

Bug: 188871598
Test: build
Change-Id: I358c19c91e8b20d47967aa3b26a8aa5dd6a97ab6