Before of this change, many specific classes to VirtIO were in the
Kernel namespace, which polluted it.
Everything should be more organized now, but there's still room for
improvement later.
This class member was used only to determine the device type when
printing messages to the debug log. Instead, remove this class member,
and add a quick way to find the device type according to how the VirtIO
specification says to do that.
This simplifies construction of VirtIODevices a bit, because now the
constructor doesn't need to ask for a String identified with the device
type.
