bootchart: add policy rules for bootchart

allow the bootchart to create dir and files at init,
also allow user to create the stop and start file under
/data/bootchart directory to start and stop bootchart

Change-Id: Icfee8dcd17366383eef00fbe3139744bf4427a6b
Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>