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