perf/x86/amd/iommu: Do not register a task ctx for uncore like PMUs

The new sanity check introduced by:

  26657848 ("perf/core: Verify we have a single perf_hw_context PMU")

... triggered on the AMD IOMMU driver.

IOMMUs are not per logical CPU, they cannot have per-task counters. Fix it.
Reported-by: Borislav Petkov <bp@alien8.de>
Tested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: jroedel@suse.de
Cc: suravee.suthikulpanit@amd.com
Link: http://lkml.kernel.org/r/20160423224255.GB3430@twins.programming.kicks-ass.netSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/events/amd/iommu.c

@@ -474,6 +474,7 @@ static __init int _init_perf_amd_iommu(
 
 static struct perf_amd_iommu __perf_iommu = {
 	.pmu = {
+		.task_ctx_nr    = perf_invalid_context,
 		.event_init	= perf_iommu_event_init,
 		.add		= perf_iommu_add,
 		.del		= perf_iommu_del,