Add west.yml configuring zephyr dependencies from sof

Added west.yaml file, that manages zephyr repo and its dependencies.
Additionally west manifest may now control sof submodules.
Added submanifests directory with README.txt file so the
submanifests directory exists in version control - otherwise
west update command returns error. This is bug described in
https://github.com/zephyrproject-rtos/west/issues/594 .

Co-developed-by: Andrey Borisovich <andrey.borisovich@intel.com>
Signed-off-by: Andrey Borisovich <andrey.borisovich@intel.com>
Signed-off-by: Krzysztof Frydryk <krzysztofx.frydryk@intel.com>

submanifests/README.txt

@@ -0,0 +1,12 @@
+This directory can contain additional west manifest files. Any files
+in this directory will be included in the main west.yml file sorted by
+filename.
+
+For more details about how this works, see this part of the west
+documentation:
+
+https://docs.zephyrproject.org/latest/guides/west/manifest.html#example-2-2-downstream-with-directory-of-manifest-files
+
+Note: do not delete this file if there is no other content in submanifests directory.
+Submanifests directory must exist for west update command to work (even if does not contain any actual manifests).
+This is a known bug, see: https://github.com/zephyrproject-rtos/west/issues/594

west.yml

@@ -0,0 +1,38 @@
+# SOF west manifest
+manifest:
+  defaults:
+    remote: thesofproject
+
+  remotes:
+    - name: thesofproject
+      url-base: https://github.com/thesofproject
+    - name: zephyrproject
+      url-base: https://github.com/zephyrproject-rtos
+
+  projects:
+    - name: rimage
+      repo-path: rimage
+      path: sof/rimage
+      revision: 02abc5d342a3ee6965bdc933ea1439d85d0256da
+
+    - name: tomlc99
+      repo-path: tomlc99
+      path: sof/rimage/tomlc99
+      revision: e3a03f5ec7d8d33be705c5ce8a632d998ce9b4d1
+
+      # west update will override your local changes to this revision
+    - name: zephyr
+      repo-path: zephyr
+      revision: 63a497280f22aea39793dd9de9731469a83ce533
+      remote: zephyrproject
+      import:
+        name-whitelist:
+          - hal_xtensa
+          - mbedtls
+          - mipi-sys-t
+          - lz4
+          - tinycrypt
+
+  self:
+    path: sof
+    import: submanifests