perf script: Enable printing of interrupted machine state

This patch adds the output of the interrupted machine state (iregs) to
perf script. It presents them  as NAME:VALUE so this is easy to parse
during post processing.

To capture the interrupted machine state:
   $ perf record -I ....

to display iregs, use the -F option:

   $ perf script -F ip,iregs
   40afc2   AX:0x6c5770    BX:0x1e    CX:0x5f4d80a    DX:0x101010101010101    SI:0x1

Signed-off-by: Stephane Eranian <eranian@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1441039273-16260-2-git-send-email-eranian@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>