These two fields help to give more information about the device been
hotplug/hotunplug to callbacks.
There is already `dev' of type `libxl__device', but it is mostly
useful when the backend/frontend is xenstore. Some device (like
`usbdev') don't have devid, so `dev' can't be used.
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>