We need to disable per-vCPU events on a vCPU that is hot-unplugged to
keep the dynamic event state global counters consistent.

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
Message-id: 148278748055.1404.1570530281528619895.stgit@fimbulvetr.bsc.es
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>