perf report: Display user/kernel differentiator

Before:

    25.96%  copy_user_generic_string
    15.23%  two_op
    15.19%  one_op
     6.92%  enough_duration
     1.23%  alloc_pages_current
     1.14%  acpi_os_read_port
     1.08%  _spin_lock

After:

    25.96%  [k] copy_user_generic_string
    15.23%  [.] two_op
    15.19%  [.] one_op
     6.92%  [.] enough_duration
     1.23%  [k] alloc_pages_current
     1.14%  [k] acpi_os_read_port
     1.08%  [k] _spin_lock

The '[k]' differentiator is a quick clue that it's a kernel symbol,
without having to bring in the full dso column.

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>