Special case uncore_ prefix in PMU match, to allow for shorter event
uncore specifications.

Before:

  perf stat -a -e uncore_cbox/event=0x35,umask=0x1,filter_opc=0x19C/ sleep 1

After

  perf stat -a -e cbox/event=0x35,umask=0x1,filter_opc=0x19C/ sleep 1

Committer tests:

   # perf list uncore

  List of pre-defined events (to be used in -e):

    uncore_cbox_0/clockticks/                       [Kernel PMU event]
    uncore_cbox_1/clockticks/                       [Kernel PMU event]
    uncore_imc/data_reads/                          [Kernel PMU event]
    uncore_imc/data_writes/                         [Kernel PMU event]

  # perf stat -a -e cbox_0/clockticks/ sleep 1

   Performance counter stats for 'system wide':

  281,474,976,653,084      cbox_0/clockticks/

       1.000870129 seconds time elapsed

  #
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: http://lkml.kernel.org/r/20170320201711.14142-7-andi@firstfloor.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>