Merge remote-tracking branch 'remotes/kraxel/tags/usb-20190529-pull-request' into...

usb-hub: port count config option, emulate power switching, cleanups.
usb-tablet, usb-host: bugfixes.

# gpg: Signature made Wed 29 May 2019 07:28:18 BST
# gpg:                using RSA key 4CB6D8EED3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>" [full]
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>" [full]
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>" [full]
# Primary key fingerprint: A032 8CFF B93A 17A7 9901  FE7D 4CB6 D8EE D3E8 7138

* remotes/kraxel/tags/usb-20190529-pull-request:
  usb-tablet: fix serial compat property
  usb-hub: emulate per port power switching
  usb-hub: add usb_hub_port_update()
  usb-hub: add helpers to update port state
  usb-hub: make number of ports runtime-configurable
  usb-hub: tweak feature names
  usb-host: avoid libusb_set_configuration calls
  usb-host: skip reset for untouched devices
  usb: call reset handler before updating state

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