perf script: Add the offset field specifier

Add the offset field specifier 'symoff' to show the offset from
the symbols in the output of perf-script. We can get the more
detailed address information.

Output sample:
ffffffff81467612 irq_return+0x0 => 301ec016b0 _start+0x0
ffffffff81467612 irq_return+0x0 => 301ec016b0 _start+0x0
      301ec016b3 _start+0x3     => 301ec04b70 _dl_start+0x0
ffffffff81467612 irq_return+0x0 => 301ec04b70 _dl_start+0x0
ffffffff81467612 irq_return+0x0 => 301ec04b96 _dl_start+0x26
ffffffff81467612 irq_return+0x0 => 301ec04b9d _dl_start+0x2d
      301ec04beb _dl_start+0x7b => 301ec04c0d _dl_start+0x9d
      301ec04c11 _dl_start+0xa1 => 301ec04bf0 _dl_start+0x80
[snip]

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: yrl.pp-manager.tt@hitachi.com
Link: http://lkml.kernel.org/r/20120130044314.2384.67094.stgit@linux3
Signed-off-by: Akihiro Nagai <akihiro.nagai.hw@hitachi.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>