perf report: Add --num-thread option to control number of thread

The --num-thread is to control number of thread to process events when
--multi-thread option is enabled.  Default value is the number of cpu
on the system that runs perf report.  The config variable
'report.num-thread' is also added to set a different default value.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
4 files changed