Merge remote-tracking branch 'remotes/kraxel/tags/pull-usb-20170223-1' into staging

usb: ohci bugfix, switch core to unrealize, xhci property cleanup

# gpg: Signature made Thu 23 Feb 2017 15:37:57 GMT
# gpg:                using RSA key 0x4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/pull-usb-20170223-1:
  xhci: properties cleanup
  usb: ohci: fix error return code in servicing td
  usb: replace handle_destroy with unrealize

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