We have something like this in our kernel since many months.  It sets the
console device to what OF uses.  ppc64 does the same, and it works ok.
serial is found on CHRP, ch-a is used on all powermacs.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>