Add abililty to specify USB device by /dev/bus/usb/xxx/yyy instead of VID/PID to usbtool

[M-a-r-k]

In usbtool, it would be useful to have the ability to instead of specifying the USB device by VID/PID, be able to give a path like /dev/bus/usb/005/004 (for example).

That could allow usbtool to be used with Cypress EZ-USB devices, where once you download "vend_ax.hex", they only respond to a small number of USB requests. It's not possible to query manufacturer strings etc. from the device in that state, hence usbtool can't be used with it. At least, I think that's why I couldn't get it to work...