Connect iSeries up to the standard early debugging infrastructure.

To actually use this you need to enable the iSeries early debugging
in setup_64.c. Then after the messages are logged hit Ctrl-x Ctrl-x on
your console to dump the Hypervisor console buffer.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>