Single XML package rather than one per platform

This saves us a *lot* of copy&pasted build foo and replaces it with a couple
of config options that can be set in menuconfig.

This makes adding a new platform a much smaller operation, requiring fewer
changes that are scattered throughout the buildroot tree.

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/openpower/configs/openpower_mambo_defconfig b/openpower/configs/openpower_mambo_defconfig
index ddd82fb..d87c8c3 100644
--- a/openpower/configs/openpower_mambo_defconfig
+++ b/openpower/configs/openpower_mambo_defconfig
@@ -44,3 +44,4 @@
 BR2_PACKAGE_PETITBOOT=y
 # BR2_PACKAGE_OCC is not set
 # BR2_PACKAGE_IMA_CATALOG is not set
+# BR2_PACKAGE_MACHINE_XML is not set
\ No newline at end of file