package/s390-tools: add libxml2 optional dependency

libxml2 is an optional dependency which is enabled by default since
version 2.17.0 and
https://github.com/ibm-s390-linux/s390-tools/commit/56fecf1832c3ebc4626ddf5c598762833c362d5e

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

package/s390-tools/s390-tools.mk

@@ -56,6 +56,15 @@ else
 S390_TOOLS_MAKE_OPTS += HAVE_GLIB2=0
 endif
 
+ifeq ($(BR2_PACKAGE_LIBXML2),y)
+S390_TOOLS_DEPENDENCIES += libxml2
+S390_TOOLS_MAKE_OPTS += \
+	HAVE_LIBXML2=1 \
+	XML2_CONFIG=$(STAGING_DIR)/usr/bin/xml2-config
+else
+S390_TOOLS_MAKE_OPTS += HAVE_LIBXML2=0
+endif
+
 ifeq ($(BR2_PACKAGE_NCURSES),y)
 S390_TOOLS_DEPENDENCIES += ncurses
 S390_TOOLS_MAKE_OPTS += HAVE_NCURSES=1