khadas-edge2: remove legacy uboot

[efectn]

Description

Remove Khadas Edge 2 vendor uboot support as it is broken on recent builds and mainline uboot also has similar functionalities including kbi command with patch.

GitHub issue reference:
Jira reference number [AR-9999]

Documentation summary for feature / change

Please delete this section if entry to main documentation is not needed.

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How Has This Been Tested?

• Tested SD boot
• Tested eMMC boot

Checklist:

Please delete options that are not relevant.

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

Summary by CodeRabbit

• Chores
  • Simplified Khadas Edge2 bootloader configuration to consistently use mainline U-Boot settings, removing conditional boot mechanisms and streamlining the boot setup process.

[coderabbitai]

📝 Walkthrough

Walkthrough

The pull request removes a branch-specific U-Boot setup function from the Khadas Edge2 board configuration and consolidates its logic into a mainline U-Boot override function, eliminating branch-based conditionals and simplifying the boot configuration flow.

Changes

Cohort / File(s)	Summary
U-Boot Configuration Consolidation config/boards/khadas-edge2.conf	Removed post_family_config__uboot_kedge2() function that conditionally gated factory-style U-Boot setup; streamlined post_family_config__kedge2_use_mainline_uboot() to unconditionally apply mainline U-Boot overrides with boot-related parameters (BOOTCONFIG, BOOTDELAY, BOOTSOURCE, BOOTBRANCH, BOOTPATCHDIR, BOOTDIR, UBOOT_TARGET_MAP).

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 Simplify, simplify, the rabbit does say,
Remove the old branches that clutter the way,
Mainline U-Boot flows, so clean and so bright,
Khadas Edge2 boots true, configuration made right! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically summarizes the main change: removing legacy U-Boot support for the Khadas Edge2 board.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[github-actions]

✅ This PR has been reviewed and approved — all set for merge!