[IA64] Remove needless delay in MCA rendezvous

While testing the MCA recovery code, noticed that some machines would have a
five second delay rendezvousing cpus.  What was happening is that
ia64_wait_for_slaves() would check to see if all the slave CPUs had
rendezvoused.  If any had not, it would wait 1 millisecond then check again.
If any CPUs had still not rendezvoused, it would wait 5 seconds before
checking again.

On some configs the rendezvous takes more than 1 millisecond, causing the code
to wait the full 5 seconds, even though the last CPU rendezvoused after only
a few milliseconds.

The fix is to check every 1 millisecond to see if all the cpus have
rendezvoused.  After 5 seconds the code concludes the CPUs will never
rendezvous (same as before).

The MCA code is, by definition, not performance critical, but a needless
delay of 5 seconds is senseless.  The 5 seconds also adds up quickly
when running the error injection code in a loop.

This patch both simplifies the code and removes the needless delay.

Signed-off-by: Russ Anderson <rja@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>