[ArmBackend] Fix in setup.sh for MacOS

[freddan80]

Make sure setup continues if FVP's are already installed

cc @digantdesai @per @zingo @oscarandersson8218 @mergennachin @byjlw

[pytorch-bot]

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❌ 1 New Failure, 1 Cancelled Job

As of commit efbe965 with merge base 883ff14 ():

NEW FAILURE - The following job has failed:

• Check Labels / Check labels (gh)
  RuntimeError: Error checking labels: PR does not have required labels

CANCELLED JOB - The following job was cancelled. Please retry:

• trunk / test-models-macos (cmake, llama2, portable, macos-m1-stable, 90) / macos-job (gh)
  ##[error]The operation was canceled.

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[zingo]

macos fail unrelated