x86: UV BAU messaging timeouts

This patch replaces a 'nop' uv_enable_timeouts() in the
UV TLB shootdown code. (somehow, long ago that function got
eviscerated)

If any cpu in the destination node does not get interrupted by the
message and post completion in a reasonable time the hardware
should respond to the sender with an error.  This function
enables such timeouts.

Tested on the UV hardware simulator.

Signed-off-by: Cliff Wickman <cpw@sgi.com>
LKML-Reference: <E1LpjXU-00007e-Qh@eag09.americas.sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>