Arm backend: Make the logic for temp_allocation_pool realistic

[gggekov]

• Move the setting of ETHOSU_MODEL & ETHOSU_ARENA from corstone_utils.cmake to the top-level app CMake so that the linker script is correctly generated. As a result, the .bss.tensor section, used for the temp_allocation_pool, goes into the SRAM instead of the DDR for Shared_Sram.
• Use 2MB of temp_allocation_pool for Corstone-300 and 4MB-64KB of temp_allocation_pool for Corstone-320.
• Remove the specify_ethosu_scratch option
• Change default memory mode for the Ethos-U85 to Dedicated_Sram in order to match how we build the
  arm_executor_runner binary

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

[pytorch-bot]

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[Copilot]

Pull request overview

This PR updates the Arm bare-metal Ethos-U runner configuration to make temp_allocation_pool sizing and placement align with realistic Corstone SRAM constraints, and simplifies the flow by removing the dynamic “derive scratch size from PTE” option.

Changes:

• Remove the --specify_ethosu_scratch option from scripts/tests and stop deriving scratch size from PTEs.
• Set more realistic default ET_ARM_BAREMETAL_SCRATCH_TEMP_ALLOCATOR_POOL_SIZE values based on SYSTEM_CONFIG + MEMORY_MODE.
• Move ETHOSU_MODEL / ETHOSU_ARENA handling to the top-level runner CMake so linker script preprocessing gets the correct values.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
examples/arm/run.sh	Removes --specify_ethosu_scratch support and adds extra configure logging.
examples/arm/executor_runner/CMakeLists.txt	Adjusts default scratch pool sizing and pre-processes linker scripts with ETHOSU_MODEL/ARENA based on memory mode.
backends/arm/test/test_model.py	Removes the PTE-derived scratch sizing option and associated build logic.
backends/arm/test/common.py	Updates the default U85 memory mode and extra flags used by tests.
backends/arm/scripts/get_ethosu_scratch_from_pte.py	Improves bundled-program detection and adjusts output formatting.
backends/arm/scripts/corstone_utils.cmake	Removes ETHOSU_MODEL/ARENA compile definitions from the Corstone helper target.

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