Make packagemanager_aidl available to Virt APEX

Even though the interface is unstable, it's okay to be used by the Virt
APEX since the apex itself is unstable(and not-updatable) as well. We
need to stabilize the interface when making the apex updatable.

Bug: 199146189
Test: m
Change-Id: Idd98e3d1876b83a357f50ac8892ecdde871a616c