usb: Add basic code to emulate Chipidea USB IP

usb: Add basic code to emulate Chipidea USB IP

Add code to emulate Chipidea USB IP (used in i.MX SoCs). Tested to
work against:

-usb -drive if=none,id=stick,file=usb.img,format=raw -device \
 usb-storage,bus=usb-bus.0,drive=stick

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
Cc: Marcel Apfelbaum <marcel.apfelbaum@zoho.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: qemu-devel@nongnu.org
Cc: qemu-arm@nongnu.org
Cc: yurovsky@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>