fix(ports): move tx_initialize_low_level.S to example_build for M33/M55/M85 GNU

[nhuvaoanh123]

Summary

Fixes #452

The Cortex-M33, M55, and M85 GNU ports incorrectly include tx_initialize_low_level.S as a library source in CMakeLists.txt. This file is board-specific initialization code that users must customize for their hardware. Including it in the library causes linker conflicts (duplicate symbol _tx_initialize_low_level) when users provide their own implementation via CMake FetchContent.

This PR aligns these three ports with the established pattern used by Cortex-M0/M3/M4/M7 GNU ports:

• Move tx_initialize_low_level.S from src/ to example_build/ (reference template only)
• Remove the tx_initialize_low_level.S entry from CMakeLists.txt target_sources
• Add sample_threadx.c to example_build/ for consistency with other ports
• Align CMakeLists.txt formatting with the {{BEGIN/END_TARGET_SOURCES}} markers used by other ports

Ports affected

Port	Before	After
cortex_m33/gnu	src/ + in CMake	example_build/ only
cortex_m55/gnu	src/ + in CMake	example_build/ only
cortex_m85/gnu	src/ + in CMake	example_build/ only

Reference (correct pattern)

• ports/cortex_m4/gnu/ — tx_initialize_low_level.S in example_build/, not referenced in CMakeLists.txt

Test plan

• Verify CMakeLists.txt no longer references tx_initialize_low_level.S
• Verify example_build/ contains tx_initialize_low_level.S + sample_threadx.c for all three ports
• Verify CMake FetchContent integration builds without duplicate symbol errors
• CI passes on Cortex-M33/M55/M85 targets

Signed-off-by: An Dao webmaster@taktflow-systems.com

[fdesbiens]

Thank you for this contribution, @nhuvaoanh123.

Before we can accept it, you need to sign the Eclipse Contributor Agreement (ECA). The purpose of the ECA is to provide a written record that you have agreed to provide your code and documentation contributions under the licenses used by the Eclipse ThreadX project. It also makes it clear that you are promising that what you are contributing to Eclipse is code you wrote, and you have the necessary rights to contribute it to our projects. And finally, it documents a commitment from you that your open source contributions will be permanently on the public record.

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[nhuvaoanh123]

Thanks @fdesbiens! I've signed the ECA using webmaster@taktflow-systems.com and my GitHub ID nhuvaoanh123 is linked to my Eclipse account. The ECA check should pass on re-run. Please let me know if anything else is needed.

[fdesbiens]

@nhuvaoanh123, I checked your Eclipse account, and there is no GitHub ID in it. Can you please add it? Otherwise, our backend system cannot sync with GitHub.

[nhuvaoanh123]

Hi @fdesbiens, I have now linked my GitHub ID (nhuvaoanh123) to my Eclipse account. Could you please check again? The account was signed with the same email address used for my Git commits. Thank you!