[zorg] Add Arm-managed workers for AArch64 SVE/SVE2 builders (#913)

We are migrating the AArch64 SVE builders from Linaro-hosted
infrastructure to Arm-hosted infrastructure.

Add the new Arm-managed workers to the existing AArch64 SVE/SVE2
builders. Reusing the existing builders avoids introducing duplicate
builders during the transition and keeps the builder names unchanged.

The new workers will initially connect to the silent Buildbot master for
validation. Once the existing Linaro workers have been taken offline,
the Arm workers can be connected to the normal master.

The Linaro worker configuration can be removed separately, once the
migration is complete.