LU-12275 sec: ioctls to handle encryption policies

LU-12275 sec: ioctls to handle encryption policies

Introduce support for fscrypt IOCTLs that handle encryption
policies v2. It enables setting/getting encryption policies on
individual directories, letting users decide how they want to
encrypt specific directories.

fscrypt encryption policies v2 are supported from Linux 5.4.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I0dc8c9ca1291ddd9c44617feb5df845b57d7dcc9
Reviewed-on: https://review.whamcloud.com/37673
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>