bootstat write timing to the kernel. BUG=chromium-os:19176 TEST=Test it on ChromeOS, and /sys/kernel/debug/bootstat/report contains all timings written by bootstat. Change-Id: I25a2e0aec1b24f52047c7bc97f0ad40f78009a8b Reviewed-on: http://gerrit.chromium.org/gerrit/6598 Reviewed-by: Simon Glass <[email protected]> Tested-by: Da Zheng <[email protected]>