x86, UV: BAU broadcast to the local hub

Make the Broadcast Assist Unit driver use the BAU for TLB
shootdowns of cpu's on the local uvhub.

It was previously thought that IPI might be faster to the cpu's
on the local hub.  But the IPI operation would have to follow
the completion of the BAU broadcast anyway.  So we broadcast to
the local uvhub in all cases except when the current cpu was the
only local cpu in the mask.

This simplifies uv_flush_send_and_wait() in that it returns
either all shootdowns complete, or none.

Adjust the statistics to account for shootdowns on the local
uvhub.

Signed-off-by: Cliff Wickman <cpw@sgi.com>
Cc: gregkh@suse.de
LKML-Reference: <E1OJvNy-0004aq-G7@eag09.americas.sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>