[IA64] kdump: add kdump_on_fatal_mca

While it is convenient that we can invoke kdump by asserting INIT
via button on chassis etc., there are some situations that invoking
kdump on fatal MCA is not welcomed rather than rebooting fast without
dump.

This patch adds a new flag 'kdump_on_fatal_mca' that is independent
from 'kdump_on_init' currently available.  Adding this flag enable
us to turning on/off of kdump depend on the event, INIT and/or fatal
MCA.  Default for this flag is to take the dump.

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