Merge remote-tracking branch 'remotes/sstabellini/tags/xen-20160126-2' into staging

Xen 2016/01/26 with Signed-off-by lines.

# gpg: Signature made Tue 26 Jan 2016 17:20:12 GMT using RSA key ID 70E1AE90
# gpg: Good signature from "Stefano Stabellini <stefano.stabellini@eu.citrix.com>"

* remotes/sstabellini/tags/xen-20160126-2:
  xen: make it possible to build without the Xen PV domain builder
  xen: domainbuild: reopen libxenctrl interface after forking for domain watcher.
  xen: Use stable library interfaces when they are available.
  xen: Switch uses of xc_map_foreign_{pages,bulk} to use libxenforeignmemory API.
  xen: Switch uses of xc_map_foreign_range into xc_map_foreign_pages
  xen: Switch to libxengnttab interface for compat shims.
  xen: Switch to libxenevtchn interface for compat shims.
  xen_console: correctly cleanup primary console on teardown.

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