Arm backend: Add target tests for cond and while.

[Erik-Lundell]

Currently only Ethos-U85 supports the operators.

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

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[zingo]

OK to merge when testfails in Arm backend are fixed

[zingo]

Fix for
2025-12-29T09:55:37.9183294Z [check] model_pte_program_size: 3056 bytes <= 3000 B -> FAIL
Was just merged so a rebase will probably fix that.
Left is only:

FAILED backends/arm/test/ops/test_cond.py::test_cond_u85_INT[one_arg_and_scalar_one_output] - RuntimeError: FoldAndAnnotateQParamsPass: Input qparams do not match
FAILED backends/arm/test/ops/test_cond.py::test_cond_u85_INT[nested_one_arg_one_output] - Exception: An error occurred when running the 'DuplicateDQPass' pass after the following passes: []