meta-ohos-staging: add layer to stage changes before upstreaming

While some changes could go upstream righ away, some others might need
more work until ready. This layer gives us a space to keep these recipes
and changes while we get them ready.

Signed-off-by: Stefan Schmidt <stefan.schmidt@huawei.com>

meta-ohos-staging/README.md

+This README file contains information on the contents of the meta-ohos-staging layer.
+
+Table of Contents
+=================
+
+  I. Adding the meta-ohos-staging layer to your build
+ II. Misc
+
+
+I. Adding the meta-ohos-staging layer to your build
+===================================================
+
+This layer only depends on poky or oe-core. To add it to your layers:
+
+Run 'bitbake-layers add-layer meta-ohos-staging'
+
+II. Misc
+========
+
+This layer provides recipes intended to upstream into other layer, but are not
+fully ready yet. As a start we will have some connectivity related recipes for
+OpenThread as well as MQTT.

meta-ohos-staging/conf/layer.conf

+# We have a conf directory, add to BBPATH
+BBPATH .= ":${LAYERDIR}"
+
+# We have recipes-* directories, add to BBFILES
+BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
+            ${LAYERDIR}/recipes-*/*/*.bbappend"
+
+BBFILE_COLLECTIONS += "meta-ohos-staging"
+BBFILE_PATTERN_meta-ohos-staging = "^${LAYERDIR}/"
+BBFILE_PRIORITY_meta-ohos-staging = "5"
+
+LAYERDEPENDS_meta-ohos-staging = "core"
+LAYERSERIES_COMPAT_meta-ohos-staging = "dunfell"