meta-phosphor: nuvoton-layer: add gpio-keys kernel feature

The phosphor-base.inc distro file enables the phosphor-gpio-keys
KERNEL_FEATURE. Add support for this feature to the linux-nuvoton recipe
via a bbappend in meta-phosphor's nuvoton layer.

Tested: Built and ran on NPCM750 EVB

Change-Id: Id957c6209ebb841fce2cdad1cc0790e0d58da60c
Signed-off-by: Benjamin Fair <benjaminfair@google.com>
diff --git a/nuvoton-layer/recipes-kernel/linux/linux-nuvoton/phosphor-gpio-keys.scc b/nuvoton-layer/recipes-kernel/linux/linux-nuvoton/phosphor-gpio-keys.scc
new file mode 100644
index 0000000..78961af
--- /dev/null
+++ b/nuvoton-layer/recipes-kernel/linux/linux-nuvoton/phosphor-gpio-keys.scc
@@ -0,0 +1,2 @@
+define KFEATURE_DESCRIPTION "Enable gpio-keys"
+kconf non-hardware phosphor-gpio-keys.cfg