package/xserver_xorg-server: fix init script conflicts

xdm package also installs a init script that utimately starts X server

Signed-off-by: Yanghao Cheng <yanghao.cheng@aioi-atg.com>
[yann.morin.1998@free.fr:
  - don't use $(or ...)
  - slightly reword comment
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit f9cd15446744c45cf35792d4560e1c1da448502b)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/x11r7/xserver_xorg-server/xserver_xorg-server.mk

@@ -181,8 +181,9 @@ define XSERVER_XORG_SERVER_INSTALL_INIT_SYSTEMD
 		$(TARGET_DIR)/usr/lib/systemd/system/xorg.service
 endef
 
-# init script conflicts with S90nodm
-ifneq ($(BR2_PACKAGE_NODM),y)
+# Install the init script only when neither nodm nor xdm are enabled, as
+# they would be responsible for starting the server.
+ifeq ($(BR2_PACKAGE_NODM)$(BR2_PACKAGE_XAPP_XDM),)
 define XSERVER_XORG_SERVER_INSTALL_INIT_SYSV
 	$(INSTALL) -D -m 755 package/x11r7/xserver_xorg-server/S40xorg \
 		$(TARGET_DIR)/etc/init.d/S40xorg