PFT (Per-File-Encryption Tagger) driver architecture document.

PFT is a new driver, a part of the Per-File-Encryption solution.

Platforms supported: MSM8974, MSM8994, MSM8996
Location: security/pfe

Change-Id: Iec1a2584fec82345fd4b081da18e9090be1b677f
Signed-off-by: Nir Ofry <nofry@codeaurora.org>
Signed-off-by: Andrey Markovytch <andreym@codeaurora.org>