Merge remote-tracking branch 'remotes/sstabellini/tags/xen-migration-2.4-tag' into staging

xen-migration-2.4

# gpg: Signature made Mon 03 Aug 2015 17:18:36 BST using RSA key ID 70E1AE90
# gpg: Good signature from "Stefano Stabellini <stefano.stabellini@eu.citrix.com>"

* remotes/sstabellini/tags/xen-migration-2.4-tag:
  migration: Fix regression for xenfv and pc,accel=xen machine.
  migration: Fix global state with Xen.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>