meta-ohos-core: Introduce core layer

Add meta-ohos-core layer skeleton.
It is intended to be used to provide OpenHarmony
distributions and images.

Signed-off-by: Zbigniew Bodek <zbigniew.bodek@huawei.com>

meta-ohos-core/README.md

+This README file contains information about the contents of the meta-ohos-core layer.
+
+Please see the corresponding sections below for details.
+
+Table of Contents
+=================
+
+  I. Dependencies
+ II. Adding the meta-ohos-core layer to your build
+III. Misc
+
+I. Dependencies
+===============
+
+This layer depends on:
+
+- URI: git://git.yoctoproject.org/poky
+  - branch: master
+  - revision: HEAD
+
+- URI: git://git.openembedded.org/meta-openembedded
+  - layers: meta-oe
+  - branch: master
+  - revision: HEAD
+
+II. Adding the meta-ohos-core layer to your build
+=================================================
+
+Run 'bitbake-layers add-layer /path/to/meta-ohos-core'
+
+III. Misc
+=========
+
+This layer provides recipes for the core elements of the OpenHarmony distribution.

meta-ohos-core/conf/layer.conf

+# We have a conf and classes directory, add to BBPATH
+BBPATH .= ":${LAYERDIR}"
+
+# We have recipes-* directories, add to BBFILES
+BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
+            ${LAYERDIR}/recipes-*/*/*.bbappend"
+
+BBFILE_COLLECTIONS += "meta-ohos-core"
+BBFILE_PATTERN_meta-ohos-core = "^${LAYERDIR}/"
+BBFILE_PRIORITY_meta-ohos-core = "6"
+
+LAYERDEPENDS_meta-ohos-core = "core"
+LAYERSERIES_COMPAT_meta-ohos-core = "dunfell"