Add support to display hardware events translations available
through the sysfs. Add 'events' group attribute under the sysfs
x86 PMU record with attribute/file for each hardware event.

This patch adds only backbone for PMUs to display config under
'events' directory. The specific PMU support itself will come
in next patches, however this is how the sysfs group will look
like:

  # ls  /sys/devices/cpu/events/
  branch-instructions
  branch-misses
  bus-cycles
  cache-misses
  cache-references
  cpu-cycles
  instructions
  ref-cycles
  stalled-cycles-backend
  stalled-cycles-frontend

The file - hw event ID mapping is:

  file                      hw event ID
  ---------------------------------------------------------------
  cpu-cycles                PERF_COUNT_HW_CPU_CYCLES
  instructions              PERF_COUNT_HW_INSTRUCTIONS
  cache-references          PERF_COUNT_HW_CACHE_REFERENCES
  cache-misses              PERF_COUNT_HW_CACHE_MISSES
  branch-instructions       PERF_COUNT_HW_BRANCH_INSTRUCTIONS
  branch-misses             PERF_COUNT_HW_BRANCH_MISSES
  bus-cycles                PERF_COUNT_HW_BUS_CYCLES
  stalled-cycles-frontend   PERF_COUNT_HW_STALLED_CYCLES_FRONTEND
  stalled-cycles-backend    PERF_COUNT_HW_STALLED_CYCLES_BACKEND
  ref-cycles                PERF_COUNT_HW_REF_CPU_CYCLES

Each file in the 'events' directory contains the term translation
for the symbolic hw event for the currently running cpu model.

  # cat /sys/devices/cpu/events/stalled-cycles-backend
  event=0xb1,umask=0x01,inv,cmask=0x01
Suggested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1349873598-12583-2-git-send-email-jolsa@redhat.comSigned-off-by: Ingo Molnar <mingo@kernel.org>