meta-digi-dey: handle dynamic layer configuration

Patch taken from meta-mentor and meta-fsl-arm.

Signed-off-by: Javier Viguera <javier.viguera@digi.com>

meta-digi-dey/conf/layer.conf

@@ -5,6 +5,11 @@ BBPATH .= ":${LAYERDIR}"
 BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
             ${LAYERDIR}/recipes-*/*/*.bbappend"
 
+# Let us add layer-specific bbappends which are only applied when that
+# layer is included in our configuration
+BBFILES += "${@' '.join('${LAYERDIR}/other-layers/%s/recipes*/*/*.bbappend' % layer \
+               for layer in BBFILE_COLLECTIONS.split())}"
+
 BBFILE_COLLECTIONS += "dey"
 BBFILE_PATTERN_dey := "^${LAYERDIR}/"
 BBFILE_PRIORITY_dey = "6"