pft: register PFT to security framework

When PFT is the chosen Linux Security Module (LSM),
register the PFT to the security framework.
Fix pft_inode_set_xattr() definition to match
the security framework hooks.

Change-Id: I1a8efcf13aa3ca324e2c23d7cc71274b217d2aaa
Signed-off-by: Amir Samuelov <amirs@codeaurora.org>