LU-12355 llite: include file linux/selinux.h removed

LU-12355 llite: include file linux/selinux.h removed

In kernel 5.1 linux/selinux.h was removed with
SELinux: Remove unused selinux_is_enabled

Linux-commit: 3d252529480c68bfd6a6774652df7c8968b28e41

This patch is back-ported from the following one:
Lustre-commit: 39e5bfa73414d18738001761b42ea0e3264c2983
Lustre-change: https://review.whamcloud.com/35035

Test-Parameters: trivial
Signed-off-by: Shaun Tancheff <stancheff@cray.com>
Change-Id: If963e6b22b7b07899de5b970f934bb157c5f7cec
Reviewed-on: https://review.whamcloud.com/38480
Reviewed-by: Petros Koutoupis <petros.koutoupis@hpe.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>