ext4: Set the bio REQ_NOENCRYPT flag

Sets the REQ_NOENCRYPT flag for I/O requests that ext4 has already
encrypted.  Lower layers such as dm-crypt can observe that flag to
avoid encrypting again if that's how the user configures the
environment.

Change-Id: I62a93e480a9f5788070446bd94694dfb9f83c277
Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Git-repo: https://android.googlesource.com/kernel/common/


Git-commit: 7af2a1358e1577379c04d08b5c1d2ac4565c9418
[stummala@codeaurora.org: resolve merge conflicts]
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>