xhci: properties cleanup

xhci: properties cleanup

Split xhci properties into common and nec specific.

Move the backward compat flags to nec, so the new qemu-xhci
devices doesn't carry on the compatibiity stuff.

Move the msi/msix switches too and just enable msix for qemu-xhci.

Also move the intrs and slots properties.  Wasn't a great idea to
make them configurable in the first place, nobody needs this.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1487663432-10410-1-git-send-email-kraxel@redhat.com