Processor assignments for PORT, VIRQ and IPI interrupts were all being
handled separately. Merge these together to shrink the code.
PORT channels previously hadn't been attempting intr_event_bind(). This
appears to have been missed during development, so add this to ensure
consistency with other event channel types.
Due to needing to recover from intr_event_bind() failing,
xen_intr_bind_virq() and xen_intr_alloc_and_bind_ipi() could call
xen_intr_unbind(). With the intr_event_bind() call removed there is no
longer any potential need to call xen_intr_unbind().
Fixes: f229f35db70f ("xen/intr: balance dynamic interrupts across available vCPUs")