buildroot

logrotate: enable selinux support

Selinux is currently disabled staticly in logrotate. This patch fixes
this by checking for libselinux and adding it as a dependecy if it has
been selected.

Signed-off-by: Adam Duskett <Adamduskett@outlook.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>