f2fs: ice: snapshot of ICE related changes for F2FS

This is a snapshot of the ICE related changes required
for F2FS as of msm-4.14 commit 6fb74ab56(f2fs/fscrypt-ice:
allow merging some IOs).

Change-Id: I92b7c71276c616668a271a3e7a20fc397c089d1c
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
Signed-off-by: Neeraj Soni <neersoni@codeaurora.org>
Signed-off-by: Barani Muthukumaran <bmuthuku@codeaurora.org>