Revert to SDK v3.1

Author: sctanf

west.yml

@@ -6,5 +6,5 @@ manifest:
     - name: sdk-nrf
       path: nrf
       url: https://github.com/nrfconnect/sdk-nrf.git
-      revision: v3.3.0-preview3-branch
-      import: true
+      revision: v3.1-branch
+      import: true