mm: mm_event: add page fault stat

mm: mm_event: add page fault stat

This patch add major and minor fault mm_event stat so that we could
keep tracking [avg|max]_latency for the handling the event
as well as count of the event.

With major fault, we could see how long the IO is delayed. It's very
tightly coupled with application's latency.

With major+minor fault, we could see how many of pages are allocated
for the process in the period. It would help to see memory spike.

Mot-CRs-fixed: (CR)

Bug: 80168800
Change-Id: I8a4434493e3ec291227961939a24c3d57a18fd5b
Signed-off-by: Minchan Kim <minchan@google.com>
Signed-off-by: Cho KyongHo <pullip.cho@samsung.com>
Reviewed-on: https://gerrit.mot.com/1453720
SME-Granted: SME Approvals Granted
SLTApproved: Slta Waiver
Tested-by: Jira Key
Reviewed-by: Xiangpo Zhao <zhaoxp3@motorola.com>
Submit-Approved: Jira Key