for-linus-4.3-rc0-tag

- Convert xen-blkfront to the multiqueue API
- [arm] Support binding event channels to different VCPUs.
- [x86] Support > 512 GiB in a PV guests (off by default as such a
  guest cannot be migrated with the current toolstack).
- [x86] PMU support for PV dom0 (limited support for using perf with
  Xen and other guests).