hw: Only compile the usb-dwc2 controller if it is really needed

hw: Only compile the usb-dwc2 controller if it is really needed

The USB_DWC2 switch is currently "default y", so it is included in all
qemu-system-* builds, even if it is not needed. Even worse, it does a
"select USB", so USB devices are now showing up as available on targets
that do not support USB at all. This sysbus device should only be
included by the boards that need it, i.e. by the Raspi machines.

Fixes: 153ef1662c ("dwc-hsotg (dwc2) USB host controller emulation")
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Paul Zimmerman <pauldzim@gmail.com>
Message-id: 20200722154719.10130-1-thuth@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>