config.json: rewrite meta-virt build steps

In the meta-virt builder, don't do a world build but instead build just
xen-image-minimal for both qemuarm64 and qemux86-64.

This can be expanded over time, but is a sensible starting point and
builds cleanly.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

config.json

@@ -934,8 +934,6 @@
         },
         "meta-virt" : {
             "NEEDREPOS" : ["poky", "meta-openembedded", "meta-virtualization"],
-            "MACHINE" : "qemux86-64",
-            "BBTARGETS" : "world -k",
             "ADDLAYER" : [
                 "${BUILDDIR}/../meta-openembedded/meta-oe",
                 "${BUILDDIR}/../meta-openembedded/meta-python",
@@ -944,8 +942,18 @@
                 "${BUILDDIR}/../meta-virtualization"
             ],
             "extravars" : [
-                "DISTRO_FEATURES:append = ' virtualization'"
-            ]
+                "DISTRO_FEATURES:append = ' virtualization xen'"
+            ],
+            "step1" : {
+                "shortname": "Xen for qemux86-64",
+                "MACHINE": "qemux86-64",
+                "BBTARGETS" : "xen-image-minimal"
+            },
+            "step2" : {
+                "shortname": "Xen for qemuarm64",
+                "MACHINE": "qemuarm64",
+                "BBTARGETS" : "xen-image-minimal"
+            }
         },
         "qa-extras" : {
             "MACHINE" : "qemux86-64",