perf report: Add -g cumulative option

The -g cumulative option is for showing accumulated overhead (period)
value as well as self overhead.

Cc: Arun Sharma <asharma@fb.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
3 files changed