perf evlist: Move event attributes to after the / when uniquefying using the PMU...

perf evlist: Move event attributes to after the / when uniquefying using the PMU name

When turning an event with attributes to the format including the PMU we
need to move the "event:attributes" format to "event/attributes/" so
that we can copy the event displayed and use it in the command line,
i.e. in 'perf top' we had:

 1K cpu_atom/cycles:P/
 11K cpu_core/cycles:P/

If I try to use that on the command line:

  # perf top -e cpu_atom/cycles:P/
  event syntax error: 'cpu_atom/cycles:P/'
                                \___ Bad event or PMU

  Unable to find PMU or event on a PMU of 'cpu_atom'

  Initial error:
  event syntax error: 'cpu_atom/cycles:P/'
                                \___ unknown term 'cycles:P' for pmu
  'cpu_atom'

  valid terms:

    event,pc,edge,offcore_rsp,ldlat,inv,umask,cmask,config,config1,config2,config3,name,period,freq,branch_type,time,call-graph,stack-size,no-inherit,inherit,max-stack,nr,no-overwrite,overwrite ,driver-config,percore,aux-output,aux-sample-size,metric-id,raw,legacy-cache,hardware
  Run
    'perf list' for a list of valid events

  Usage: perf top [<options>]

     -e, --event <event>   event selector. use 'perf list' to list available events
  #

Tested-by: Kan Liang <kan.liang@linux.intel.com>
Cc: Hector Martin <marcan@marcan.st>
Cc: Ian Rogers <irogers@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/lkml/ZXxyanyZgWBTOnoK@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>