package/dbus: select SELinux module

Select the dbus SElinux module so that it will be compiled in the
refpolicy. This way, if an SELinux policy is generated, dbus will be
supported.

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>