fs: sync: Asynchronous Fsync from HTC

    * taken from Faux's S5 repo and modified/fixed-up
      for Linux 3.10 and shamu

Change-Id: Ia1917f3def4be0c39fa867a047fa8952b7fd0f42
Conflicts:
	drivers/mmc/core/mmc.c

Original commit: https://bitbucket.org/arter97/android_kernel_samsung_exynos7420/commits/8125c532b02a7d8c36d39f18e4ffcce2180e26cc

Conflicts:
	fs/sync.c
	include/linux/fs.h