package/x11r7/xserver_xorg-server: Udev kms support depends on libdrm

Fixes
http://autobuild.buildroot.net/results/18c/18c554d148fc00f85690c1638976dd6d0d7ff219/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

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

@@ -127,6 +127,13 @@ endif
 ifeq ($(BR2_PACKAGE_HAS_UDEV),y)
 XSERVER_XORG_SERVER_DEPENDENCIES += udev
 XSERVER_XORG_SERVER_CONF_OPT += --enable-config-udev
+# udev kms support depends on libdrm
+ifeq ($(BR2_PACKAGE_LIBDRM),y)
+XSERVER_XORG_SERVER_DEPENDENCIES += libdrm
+XSERVER_XORG_SERVER_CONF_OPT += --enable-config-udev-kms
+else
+XSERVER_XORG_SERVER_CONF_OPT += --disable-config-udev-kms
+endif
 else
 ifeq ($(BR2_PACKAGE_DBUS),y)
 XSERVER_XORG_SERVER_DEPENDENCIES += dbus