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.

Bug: 120445624
Change-Id: I44476230324e9397e292328463f846af4befbd6d
[joelaf: Needed for storaged fsync accounting ("storaged --uid" and
         "storaged --task".)]
Signed-off-by: Mohan Srinivasan <srmohan@google.com>
[AmitP: Folded following android-4.9 commit changes into this patch
        a5c4dbb05ab7 ("ANDROID: Replace spaces by '_' for some
        android filesystem tracepoints.")]
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
[astrachan: Folded 63066f4acf92 ("ANDROID: fs: Refactor FS
            readpage/write tracepoints.") into this patch
Signed-off-by: Alistair Strachan <astrachan@google.com>