[zorg] Add Arm-hosted workers for 32-bit Arm builders (#925)

As part of the migration from Linaro infrastructure to Arm
infrastructure, add new Arm-managed workers for the 32-bit Arm Clang and
LLDB builders to the OSUOSL Buildbot configuration.

Add the new Arm-managed workers to the existing ARMv7/ARMv8 Clang and
LLDB 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.