[IA64] printing support for MCA/INIT

Printing message to console from MCA/INIT handler is useful,
however doing oops_in_progress = 1 in them exactly makes
something in kernel wrong. Especially it sounds ugly if
system goes wrong after returning from recoverable MCA.

This patch adds ia64_mca_printk() function that collects
messages into temporary-not-so-large message buffer during
in MCA/INIT environment and print them out later, after
returning to normal context or when handlers determine to
down the system.

Also this print function is exported for use in extensional
MCA handler. It would be useful to describe detail about
recovery.

NOTE:
I don't think it is sane thing if temporary message buffer
is enlarged enough to hold whole stack dumps from INIT, so
buffering is disabled during stack dump from INIT-monarch
(= default_monarch_init_process). please fix it in future.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Acked-by: Russ Anderson <rja@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>