Upgrade to Zephyr v4.0

Also allows to use default zcbor module again, which has been updated
by Zephyr in the meantime.

west.yml

@@ -4,18 +4,12 @@ manifest:
   remotes:
     - name: zephyrproject-rtos
       url-base: https://github.com/zephyrproject-rtos
-    - name: NordicSemiconductor
-      url-base: https://github.com/NordicSemiconductor
 
   projects:
     - name: zephyr
       remote: zephyrproject-rtos
-      revision: v3.6-branch
+      revision: v4.0-branch
       import:
         name-allowlist:
           - edtt
-    # Use Nordic repo to pull in https://github.com/NordicSemiconductor/zcbor/pull/407
-    - name: zcbor
-      remote: NordicSemiconductor
-      revision: 16648fb060d857f164635ca4e8eaa716d906d244
-      path: modules/lib/zcbor
+          - zcbor