smack: new package.

SMACK stands for Simplified Mandatory Access Control Kernel. It is a Linux
Security Module which provides a Mandatory Access Control mechanism,
like SELinux, but aiming towards simplicity.

This package provides the tools to load/unload the policy from the
kernel as well as a library allowing applications to interact with
SMACK. The proper kernel options are also set.

[Thomas:
- fixed license to be LGPLv2.1 instead of LGPLv2.1+. Even though the
  debian/copyright file has the "or later" indication, none of the .c
  source files carry it, so I suppose LGPLv2.1 is more correct.
- added !BR2_PREFER_STATIC_LIB dependency.
- added dependency on host-pkgconf, since Smack configure.ac uses
  PKG_CHECK_MODULES.]

Signed-off-by: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>