perf metricgroup: Support metric constraint

perf metricgroup: Support metric constraint

Some metric groups have metric constraints. A metric group can be
scheduled as a group only when some constraints are applied.  For
example, Page_Walks_Utilization has a metric constraint,
"NO_NMI_WATCHDOG".

When NMI watchdog is disabled, the metric group can be scheduled as a
group. Otherwise, splitting the metric group into standalone metrics.

Add a new function, metricgroup__has_constraint(), to check whether all
constraints are applied. If not, splitting the metric group into
standalone metrics.

Currently, only one constraint, "NO_NMI_WATCHDOG", is checked. Print a
warning for the metric group with the constraint, when NMI WATCHDOG is
enabled.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Link: http://lore.kernel.org/lkml/1582581564-184429-5-git-send-email-kan.liang@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>