ANDROID: fs: FS tracepoints to track IO.

Adds tracepoints in ext4/f2fs/mpage to track readpages/buffered
write()s. This allows us to track files that are being read/written
to PIDs.

Change-Id: I26bd36f933108927d6903da04d8cb42fd9c3ef3d
Signed-off-by: Mohan Srinivasan <srmohan@google.com>
Git-commit: 32cbbe59
Git-repo: https://android.googlesource.com/kernel/common/


[runminw@codeaurora.org: resolve trivial merge conflicts]
Signed-off-by: Runmin Wang <runminw@codeaurora.org>