Device code shouldn't mess with QOM property "realized" since we have
proper interfaces (merge commit 6675a653).  Commit 8ddab8dd
"usb/hcd-xhci: Split pci wrapper for xhci base model" and commit
f00ff136 "usb: hcd-xhci-sysbus: Attach xhci to sysbus device"
reintroduced two instances.  Clean them up.  Note that s->xhci is
a (bus-less) TYPE_XHCI device.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210119120151.53757-1-armbru@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>