security: Use IS_ENABLED() instead of checking for built-in or module

The IS_ENABLED() macro checks if a Kconfig symbol has been enabled
either built-in or as a module, use that macro instead of open coding
the same.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>