Adding xen plugin.

This plugin adds fields resolving for following tracepoint events:

  xen:xen_mc_entry
  xen:xen_mc_extend_args

The diff of 'perf script' output generated by old and new code: (data
was generated by 'perf record -e 'xen:*' ls')

  --- script.xen.old
  +++ script.xen.new
  -         swapper     0 [002]   136.267492: xen:xen_mc_entry: [FAILED TO PARSE] op=3 nargs=2 args=ARRAY[18, 00, 00, 00, 00, 00, 00, 00, 00, e0, d4, 4b, 04, 88, ff, ff, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00, 00]
  +         swapper     0 [002]   136.267492: xen:xen_mc_entry: op 3(stack_switch) args [18, 0, 0, 0, 0, 0]
  -            perf  1970 [008]   136.273319: xen:xen_mc_extend_args: [FAILED TO PARSE] op=1 args=16 res=1
  +            perf  1970 [008]   136.273319: xen:xen_mc_extend_args: extending op 1(mmu_update) by 16 bytes res ???

NOTE We still do not handle the 'sizeof' and fail to parse following xen
tracepoints:

  xen:xen_mmu_set_pte
  xen:xen_mmu_set_pte_atomic
  xen:xen_mmu_set_domain_pte
  xen:xen_mmu_set_pte_at
  xen:xen_mmu_set_pmd
  xen:xen_mmu_set_pud
  xen:xen_mmu_set_pgd
  xen:xen_mmu_ptep_modify_prot_start
  xen:xen_mmu_ptep_modify_prot_commit
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1386076182-14484-20-git-send-email-jolsa@redhat.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>