ext4 crypto: enable HW based encryption with ICE

Numerous changes were introduced to various layers:
Block: removed dependency on selinux module for decision on bio merge
EXT4: Added feature controlled support for HW encryption
PFK: Major re-factoring, separation to eCryptfs and EXT4 sub-layers

Change-Id: I9256c8736e1c16175fe3f94733dda430ccc57980
Signed-off-by: Andrey Markovytch <andreym@codeaurora.org>