nuvoton: enable KERNEL_DANGLING_FEATURES_WARN_ONLY

Uptream yocto recently added some new code which enforces
kernel feature validation. The commit which did this is:
https://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=095175595d9f28d5a0eb7ea520c9af0100bb8dfd

This caused OpenBMC builds to start failing with the following:
| ERROR: Feature 'phosphor-gpio-keys' not found, this will cause configuration failures.
| ERROR: Check the SRC_URI for meta-data repositories or directories that may be missing
| ERROR: Set KERNEL_DANGLING_FEATURES_WARN_ONLY to ignore this issue

OpenBMC does not utilize this aspect of the kernel-yocto.bbclass
so make it a warning only.

Tested:
Verified that the resultant build still had the expected CONFIG
options set in the linux-nuvoton .config file

See openbmc/openbmc#3690

(From meta-phosphor rev: 75a6424eec93729fd40154413b1a350b9f10fe8b)

Change-Id: I12bf3857601f186300d3b1c56c490be6e6582dda
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/meta-phosphor/nuvoton-layer/recipes-kernel/linux/linux-nuvoton_%.bbappend b/meta-phosphor/nuvoton-layer/recipes-kernel/linux/linux-nuvoton_%.bbappend
index 71e208c..88b3860 100644
--- a/meta-phosphor/nuvoton-layer/recipes-kernel/linux/linux-nuvoton_%.bbappend
+++ b/meta-phosphor/nuvoton-layer/recipes-kernel/linux/linux-nuvoton_%.bbappend
@@ -2,3 +2,11 @@
 
 SRC_URI += "file://phosphor-gpio-keys.scc"
 SRC_URI += "file://phosphor-gpio-keys.cfg"
+
+
+python () {
+    # OpenBMC loads in kernel features via other mechanisms so this check
+    # in the kernel-yocto.bbclass is not required
+    d.setVar("KERNEL_DANGLING_FEATURES_WARN_ONLY","1")
+}
+