Merge remote-tracking branch 'remotes/sstabellini/tags/xen-20160622-tag' into staging

xen-20160622

# gpg: Signature made Wed 22 Jun 2016 12:45:56 BST
# gpg:                using RSA key 0x894F8F4870E1AE90
# gpg: Good signature from "Stefano Stabellini <stefano.stabellini@eu.citrix.com>"
# Primary key fingerprint: D04E 33AB A51F 67BA 07D3  0AEA 894F 8F48 70E1 AE90

* remotes/sstabellini/tags/xen-20160622-tag:
  xen: move xen_sysdev to xen_backend.c
  xen: fix qdisk BLKIF_OP_DISCARD for 32/64 word size mix
  xen: fix style of hw/block/xen_blkif.h

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