Tweak the ia64 machine check handling code to not register new sysctl nodes

Tweak the ia64 machine check handling code to not register new sysctl nodes
while holding a spin mutex.  Instead, it now shoves the machine check
records onto a queue that is later drained to add sysctl nodes for each
record.  While a routine to drain the queue is present, it is not currently
called.

Reviewed by:	marcel