Arm backend: Add Ethos-U65 support to the arm_aot_compiler.py

[zingo]

Make it possible to generate PTE files for Ethos-U65 hardware.

cc @digantdesai @freddan80 @per @oscarandersson8218 @mansnils @Sebastian-Larsson @robell

[pytorch-bot]

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• trunk / test-torchao-huggingface-checkpoints (qwen3_4b, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc1... / linux-job (gh)
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[Copilot]

Pull request overview

Adds Ethos‑U65 target support to the Arm AOT compiler flow so users can generate delegated PTE/BPTE artifacts for Ethos‑U65 configurations.

Changes:

• Extend the AOT compiler script’s supported --target list with ethos-u65-256 and ethos-u65-512.
• Update CLI help text to include Ethos‑U65 defaults for --system_config and --memory_mode.
• Change Ethos‑U65 default Vela system_config to Ethos_U65_High_End when omitted.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
backends/arm/scripts/aot_arm_compiler.py	Adds U65 targets to CLI choices and updates help text to reflect U65 defaults.
backends/arm/ethosu/compile_spec.py	Updates the default U65 Vela system_config selection logic.

---

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[Copilot]

This PR changes the default system_config chosen for U65 targets; please add/adjust unit tests to lock in the expected default selection (e.g., asserting the generated compiler flags include the expected --system-config and --memory-mode when system_config/memory_mode are omitted).

[Copilot]

The --system_config help text uses inconsistent separators/spacing ("...Embedded'/ 'Ethos_U65_High_End' / 'Ethos_U85...") which makes it harder to read. Consider rewriting it as separate per-target defaults (U55/U65/U85) or using consistent punctuation.

Suggested change

	help="System configuration to select from the Vela configuration file (see vela.ini). This option must match the selected target, default is for an optimal system 'Ethos_U55_High_End_Embedded'/ 'Ethos_U65_High_End' / 'Ethos_U85_SYS_DRAM_Mid'",
	help="System configuration to select from the Vela configuration file (see vela.ini). This option must match the selected target. Defaults for optimal systems are: Ethos-U55: 'Ethos_U55_High_End_Embedded'; Ethos-U65: 'Ethos_U65_High_End'; Ethos-U85: 'Ethos_U85_SYS_DRAM_Mid'.",