f2fs: Set the bio REQ_NOENCRYPT flag

When lower layers such as dm-crypt observe the REQ_NOENCRYPT flag, it
helps the I/O stack avoid redundant encryption, improving performance
and power utilization.

Note that lower layers must be consistent in their observation of this
flag in order to avoid the possibility of data corruption.

Change-Id: Icf8bf3ae30395cf5428b2eae071d227e8ebe6e40
Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Git-repo: Git-repo: https://android.googlesource.com/kernel/common/


Git-commit: 56568872b546659642fe99eb4388587528e8f3cc
[stummala@codeaurora.org: resolved merge conflicts]
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>