kernel-devicetree: Fix interaction when packaging disabled

When packaging is disabled using the nopackages class, ensure we don't
add to PACKAGES. This fixes builds where we have an unpackaged kernel
alongside a packaged kernel.

(From OE-Core rev: 9cce475ffc4bd71977d8e0a31c1a4df7a2f30ef7)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit d6b114cf5a9b22688c0b59a3afc46a07450d87b5)
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/kernel-devicetree.bbclass

@@ -1,8 +1,11 @@
 # Support for device tree generation
-PACKAGES_append = " \
-    ${KERNEL_PACKAGE_NAME}-devicetree \
-    ${@[d.getVar('KERNEL_PACKAGE_NAME') + '-image-zimage-bundle', ''][d.getVar('KERNEL_DEVICETREE_BUNDLE') != '1']} \
-"
+python () {
+    if not bb.data.inherits_class('nopackages', d):
+        d.appendVar("PACKAGES", " ${KERNEL_PACKAGE_NAME}-devicetree")
+        if d.getVar('KERNEL_DEVICETREE_BUNDLE') == '1':
+            d.appendVar("PACKAGES", " ${KERNEL_PACKAGE_NAME}-image-zimage-bundle")
+}
+
 FILES_${KERNEL_PACKAGE_NAME}-devicetree = "/${KERNEL_IMAGEDEST}/*.dtb /${KERNEL_IMAGEDEST}/*.dtbo"
 FILES_${KERNEL_PACKAGE_NAME}-image-zimage-bundle = "/${KERNEL_IMAGEDEST}/zImage-*.dtb.bin"