perf pmu-events: Don't lower case MetricExpr

perf pmu-events: Don't lower case MetricExpr

This patch changes MetricExpr to be written out in the same case. This
enables events in metrics to use modifiers like 'G' which currently
yield parse errors when made lower case. To keep tests passing the
literal #smt_on is compared in a non-case sensitive way - #SMT_on is
present in at least SkylakeX metrics.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Clarke <pc@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20211126071305.3733878-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>