perf expr: Add has_event function

perf expr: Add has_event function

Some events are dependent on firmware/kernel enablement. Allow such
events to be detected when the metric is parsed so that the metric's
event parsing doesn't fail.

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Namhyung Kim <namhyung@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Sohom Datta <sohomdatta1@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Caleb Biggers <caleb.biggers@intel.com>
Cc: Edward Baker <edward.baker@intel.com>
Cc: Perry Taylor <perry.taylor@intel.com>
Cc: Samantha Alt <samantha.alt@intel.com>
Cc: Weilin Wang <weilin.wang@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Jing Zhang <renyu.zj@linux.alibaba.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Zhengjun Xing <zhengjun.xing@linux.intel.com>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Ingo Molnar <mingo@redhat.com>
Link: https://lore.kernel.org/r/20230623151016.4193660-2-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>