s390x/kvm/watchdog

1. Implement a diag288 based watchdog
2. Fix virtio-ccw BIOS for gcc >= 4.9

# gpg: Signature made Mon Jun 15 12:36:25 2015 BST using RSA key ID B5A61C7C
# gpg: Good signature from "Christian Borntraeger (IBM) <borntraeger@de.ibm.com>"

* remotes/borntraeger/tags/s390x-20150615:
  s390/bios: build with -fdelete-null-pointer-checks
  watchdog: Add new Virtual Watchdog action INJECT-NMI
  nmi: Implement inject_nmi() for non-monitor context use
  s390x/watchdog: diag288 migration support
  s390x/kvm: diag288 instruction interception and handling
  s390x/watchdog: introduce diag288 watchdog device
  watchdog: change option wording to allow for more watchdogs

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