package/xen: Force disable SDL for xen-qemu build

Fixes autobuilder issue:
http://autobuild.buildroot.net/results/8bcb80dc93d38bb38ca32ad93d52c22d1176d57e/

Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit a5dd72181e1a79ffe65c788a2c1db9acdf6aa933)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/xen/xen.mk

@@ -56,6 +56,7 @@ XEN_DEPENDENCIES += argp-standalone
 endif
 XEN_INSTALL_TARGET_OPTS += DESTDIR=$(TARGET_DIR) install-tools
 XEN_MAKE_OPTS += dist-tools
+XEN_CONF_OPTS += --with-extra-qemuu-configure-args="--disable-sdl"
 
 define XEN_INSTALL_INIT_SYSV
 	mv $(TARGET_DIR)/etc/init.d/xencommons $(TARGET_DIR)/etc/init.d/S50xencommons