package/x11r7/xserver_xorg-server: add --enable-libdrm for udev

If the libdrm package is enabled, the system is built with an udev
provider and MESA3D_DRI_DRIVER is disabled this adds a --disable-libdrm
to configure options, but udev still requires libdrm and results in a
build failure since libdrm include paths aren't filled in (missing drm.h
include error).
So add --enable-libdrm for the udev scenario to counteract the previous
--disable-libdrm.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

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

@@ -130,7 +130,7 @@ XSERVER_XORG_SERVER_CONF_OPTS += --enable-config-udev
 # udev kms support depends on libdrm
 ifeq ($(BR2_PACKAGE_LIBDRM),y)
 XSERVER_XORG_SERVER_DEPENDENCIES += libdrm
-XSERVER_XORG_SERVER_CONF_OPTS += --enable-config-udev-kms
+XSERVER_XORG_SERVER_CONF_OPTS += --enable-config-udev-kms --enable-libdrm
 else
 XSERVER_XORG_SERVER_CONF_OPTS += --disable-config-udev-kms
 endif