brcm63xx: system_layout: WE7202242SA: Adapt to R01 layout

Rename overlayA/B to overlay1/2. This is a breaking change for older R0B
boards. New boards (R01) already have overlay1/2 as name for the overlay
volumes.

Older boards need to be migrated to the new layouts manually.

    ubirename /dev/ubi0 overlayA overlay1 overlayB overlay2

iopsys-brcm63xx-arm/base-files/etc/system_layout/WE7202242SA.json

@@ -4,13 +4,13 @@
       "id": 1,
       "name": "A",
       "rootfs": "ubi:rootfs1",
-      "overlay": "ubi:overlayA"
+      "overlay": "ubi:overlay1"
     },
     {
       "id": 2,
       "name": "B",
       "rootfs": "ubi:rootfs2",
-      "overlay": "ubi:overlayB"
+      "overlay": "ubi:overlay2"
     }
   ],
   "overlay_scope": [