SGI UV: TLB shootdown using broadcast assist unit, cleanups

TLB shootdown for SGI UV.

v1: 6/2 original
v2: 6/3 corrections/improvements per Ingo's review
v3: 6/4 split atomic operations off to a separate patch (Jeremy's review)
v4: 6/12 include <mach_apic.h> rather than <asm/mach-bigsmp/mach_apic.h>
         (fixes a !SMP build problem that Ingo found)
         fix the index on uv_table_bases[blade]

Signed-off-by: Cliff Wickman <cpw@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>