fs: crypto: Add support for legacy pfk based FBE

Enable legacy method to generate aes keys derived
from nonce and master key. In private mode the keys
will be used as file encryption keys and set into
Inline Crypto Engine hardware.
This will be used to support OTA upgrades where
device were launched using legacy PFK generation
method.

Test:
1) Flashed P meta, create multiple files under /data.
2) Set PIN
3) Build R (include OTA changes) and flash
   APPS images of R except userdata and boot the device.
4) Device booted upto UI.
5) Unlock device by PIN set on P build.
6) Files created with Q build retained.
7) Created new files under /data and checked retention across
   multiple re-boots.

Change-Id: I6b4e49ed4549bf4f27ea63ab33016b00dca9fcf0
Signed-off-by: Jiten Patel <jitepate@codeaurora.org>