[IA64] Stop bogus NMI & softlockup warnings in ia64 show_mem

When dumping memory via sysrq-m it is possible to take a bogus NMI watchdog
or softlockup watchdog because the dump can take a long time on big memory
systems.

Occasionally tickle the watchdog when doing the dump.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>