Now that XSA-509 went out, here's what actually caused the issue to be
noticed, plus some follow-on cleanup.

1: x86/pass-through: defer event unlock in pt_irq_create_bind()
2: x86/pass-through: no locking around pt_irq_{create,destroy}_bind()
3: x86/vPCI: tighten locking assertions
4: vPCI: drop bogus locking assertion
5: x86/pass-through: use simpler locking primitives in pt_irq_{create,destroy}_bind()
6: x86/HVM: drop vector parameter from .pi_update_irte() hook

Jan