hw/arm: Select XLNX_USB_SUBSYS for xlnx-zcu102 machine

hw/arm: Select XLNX_USB_SUBSYS for xlnx-zcu102 machine

This machine hardcodes initialization of the USB device, so select the
corresponding Kconfig. It is not enough to have it as "default y if
XLNX_VERSAL" at usb/Kconfig because building --without-default-devices
disables the default selection resulting in:

$ ./qemu-system-aarch64 -M xlnx-zcu102
qemu-system-aarch64: missing object type 'usb_dwc3'
Aborted (core dumped)

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230208192654.8854-8-farosas@suse.de>
Message-Id: <20230503091244.1450613-8-alex.bennee@linaro.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>