Boards that do not include an USB controller should not provide
USB devices. However, when running "qemu-system-s390x -device help"
for example, there's still a usb-hub, usb-kbd, usb-mouse and
usb-tablet in the list of "supported" devices. Let's fix that
by compiling and linking the USB files only if it is really
necessary.
Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
