perf stat: Uniquify hybrid event name

It would be useful to let user know the pmu which the event belongs to.
perf-stat has supported '--no-merge' option and it can print the pmu
name after the event name, such as:

"cycles [cpu_core]"

Now this option is enabled by default for hybrid platform but change
the format to:

"cpu_core/cycles/"

If user configs the name, we still use the user specified name.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
ink: https://lore.kernel.org/r/20210427070139.25256-8-yao.jin@linux.intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>