staging: panel: register reboot

we donot need the reboot notifier in module init section, as the
notifier is used after lcd is initialized. so lets register for the
reboot notifier only after we have successfully attached to the
parallel port. and similarly unregister at detach.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Acked-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>