Merge remote-tracking branch 'remotes/cohuck/tags/s390x-20180403' into staging

- fix a memory leak in the ipl code introduced with this release
- increase timeout in the bios to avoid hangs during migration (and
  rebuild bios to activate the change)

# gpg: Signature made Tue 03 Apr 2018 09:28:30 BST
# gpg:                using RSA key DECF6B93C6F02FAF
# gpg: Good signature from "Cornelia Huck <conny@cornelia-huck.de>"
# gpg:                 aka "Cornelia Huck <huckc@linux.vnet.ibm.com>"
# gpg:                 aka "Cornelia Huck <cornelia.huck@de.ibm.com>"
# gpg:                 aka "Cornelia Huck <cohuck@kernel.org>"
# gpg:                 aka "Cornelia Huck <cohuck@redhat.com>"
# Primary key fingerprint: C3D0 D66D C362 4FF6 A8C0  18CE DECF 6B93 C6F0 2FAF

* remotes/cohuck/tags/s390x-20180403:
  pc-bios/s390-ccw: update image
  pc-bios/s390-ccw: Increase virtio timeout to 30 seconds
  hw/s390x: fix memory leak in s390_init_ipl_dev()

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