Add a dracut option --device to bring up a device in initramfs

Add a dracut option --device to bring up a device in initramfs

Kdump support dump to raw device which could be on top of complex storage
such as multipath and iscsi which are standalone dracut modules.

Add a --device option to dracut which will add the device to host_devs so
dracut can add the dependent modules automaticlly and enable them in initramfs.

--device will accept device node name as the param.

Signed-off-by: Dave Young <dyoung@redhat.com>
Tested-by: Chao Wang <chaowang@redhat.com>