Its possible that we can write to the hvc_console tty as soon it is
registered.  Recently this started happening due to (what looks like) a
change to the hotplug code.

Unfortunately at this stage we have not started the khvcd kernel thread and
oops.  The solution is to start the kernel thread before registering the
tty.
Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>