meta-phosphor: libxml2: workaround upstream inherit_defer issue

There seems to be some conflict between the new `inherit_defer` syntax
in bitbake and the class-based override we are doing for PACKAGECONFIG.
Workaround it by explicitly performing the necessary inherit.

Change-Id: I77f0021abb24b9f0b82799e8422b330cc58a618b
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/meta-phosphor/recipes-core/libxml2/libxml2_%.bbappend b/meta-phosphor/recipes-core/libxml2/libxml2_%.bbappend
index 42046b1..64b755a 100644
--- a/meta-phosphor/recipes-core/libxml2/libxml2_%.bbappend
+++ b/meta-phosphor/recipes-core/libxml2/libxml2_%.bbappend
@@ -1,2 +1,6 @@
 # OpenBMC doesn't use python anymore, so no need for libxml python bindings
 PACKAGECONFIG:remove:openbmc-phosphor:class-target = "python"
+
+# Upstream bitbake currently has a bug that requires an explicit
+# inherit here.  See https://bugzilla.yoctoproject.org/show_bug.cgi?id=15361
+inherit python3targetconfig