ANDROID: fs: sched: add a counter to track fsync

Change-Id: I6c138de5b2332eea70f57e098134d1d141247b3f
Signed-off-by: Jin Qian <jinqian@google.com>

[AmitP: Refactored changes to align with changes from upstream commit
        9a070004 ("sched/headers: Move CONFIG_TASK_XACCT bits from <linux/sched.h> to <linux/sched/xacct.h>")]
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>