fdc: Add a floppy drive qdev

Floppy controllers automatically create two floppy drive devices in qdev
now. (They always created two drives, but managed them only internally.)

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 1477386868-21826-3-git-send-email-kwolf@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>