package/x11r7/xserver_xorg-server: add SELinux module

Support for xserver_xorg-server is added by the services/xserver module
in the SELinux refpolicy.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>