Merge remote-tracking branch 'remotes/kraxel/tags/pull-usb-20160803-1' into staging

usb: bugfixes for xen-usb and ehci, mingw build fix.

# gpg: Signature made Wed 03 Aug 2016 14:04:26 BST
# 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-20160803-1:
  xen: use a common function for pv and hvm guest backend register calls
  xen: drain submit queue in xen-usb before removing device
  xen: when removing a backend don't remove many of them
  ehci: faster frame index calculation for skipped frames
  wxx: Fix compilation of host-libusb.c
  wxx: Fix compiler warning for host-libusb.c

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