Adds all removable devices to the Machine menu as a Change and Eject menu
item pair. ide-cd0 would have a "Change ide-cd0..." and "Eject ide-cd0"
menu items.

Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>