perf script python: Refactor creation of perf sample dict

perf script python: Refactor creation of perf sample dict

Move the creation of the dict containing perf_sample entries into a
helper function to enable its reuse in other sample processing routines.

Signed-off-by: Arun Kalyanasundaram <arunkaly@google.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Carrillo-Cisneros <davidcc@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Seongjae Park <sj38.park@gmail.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/20170721220422.63962-3-arunkaly@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>