defconfig: Enable SELinux and its dependencies

To have more control over the access rights for different
user space needs, SELinux imposes mandatory access controls
on Linux. Which allows an administrator of a system to
define how applications and users can access different
resources such as files, devices, networks and inter-process
communication.

Change-Id: Ib5043fbacde343d547c330fbaacb435d370ea8f9
Signed-off-by: Avijit Kanti Das <avijitnsec@codeaurora.org>