[docs] Add smp boot docs for aarch64

[BernardXiong]

拉取/合并请求描述：(PR description)

[

为什么提交这份PR (why to submit this PR)

对于多核的文档一直相对比较缺少，例如smp启动

你的解决方案是什么 (what is your solution)

这是一份跟着代码走读方式的详细多核文档。

请提供验证的bsp和config (provide the config and bsp)

• BSP:

• .config:

• action:

]

当前拉取/合并请求的状态 Intent for your PR

必须选择一项 Choose one (Mandatory):

• 本拉取/合并请求是一个草稿版本 This PR is for a code-review and is intended to get feedback
• 本拉取/合并请求是一个成熟版本 This PR is mature, and ready to be integrated into the repo

代码质量 Code Quality：

我在这个拉取/合并请求中已经考虑了 As part of this pull request, I've considered the following:

• 已经仔细查看过代码改动的对比 Already check the difference between PR and old code
• 代码风格正确，包括缩进空格，命名及其他风格 Style guide is adhered to, including spacing, naming and other styles
• 没有垃圾代码，代码尽量精简，不包含#if 0代码，不包含已经被注释了的代码 All redundant code is removed and cleaned up
• 所有变更均有原因及合理的，并且不会影响到其他软件组件代码或BSP All modifications are justified and not affect other components or BSP
• 对难懂代码均提供对应的注释 I've commented appropriately where code is tricky
• 代码是高质量的 Code in this PR is of high quality
• 已经使用formatting 等源码格式化工具确保格式符合RT-Thread代码规范 This PR complies with RT-Thread code specification
• 如果是新增bsp, 已经添加ci检查到.github/ALL_BSP_COMPILE.json 详细请参考链接BSP自查

[github-actions]

👋 感谢您对 RT-Thread 的贡献！Thank you for your contribution to RT-Thread!

为确保代码符合 RT-Thread 的编码规范，请在你的仓库中执行以下步骤运行代码格式化工作流（如果格式化CI运行失败）。
To ensure your code complies with RT-Thread's coding style, please run the code formatting workflow by following the steps below (If the formatting of CI fails to run).

---

🛠 操作步骤 | Steps

1. 前往 Actions 页面 | Go to the Actions page
   点击进入工作流 → | Click to open workflow →

2. 点击 Run workflow | Click Run workflow

• 设置需排除的文件/目录（目录请以"/"结尾）
  Set files/directories to exclude (directories should end with "/")
• 将目标分支设置为 \ Set the target branch to：doc_smp_boot
• 设置PR number为 \ Set the PR number to：11057

3. 等待工作流完成 | Wait for the workflow to complete
   格式化后的代码将自动推送至你的分支。
   The formatted code will be automatically pushed to your branch.

完成后，提交将自动更新至 doc_smp_boot 分支，关联的 Pull Request 也会同步更新。
Once completed, commits will be pushed to the doc_smp_boot branch automatically, and the related Pull Request will be updated.

如有问题欢迎联系我们，再次感谢您的贡献！💐
If you have any questions, feel free to reach out. Thanks again for your contribution!

[github-actions]

📌 Code Review Assignment

🏷️ Tag: documentation

Reviewers: CXSforHPU GorrayLi lianux-mm unicornx

Changed Files (Click to expand)

• documentation/3.kernel/INDEX.md
• documentation/3.kernel/smp-startup/README.md
• documentation/3.kernel/smp-startup/README_zh.md

---

📊 Current Review Status (Last Updated: 2025-12-13 22:40 CST)

• ⌛ CXSforHPU Pending Review
• ⌛ GorrayLi Pending Review
• ⌛ lianux-mm Pending Review
• ⌛ unicornx Pending Review

---

📝 Review Instructions

1. 维护者可以通过单击此处来刷新审查状态: 🔄 刷新状态
   Maintainers can refresh the review status by clicking here: 🔄 Refresh Status

2. 确认审核通过后评论 LGTM/lgtm
   Comment LGTM/lgtm after confirming approval

3. PR合并前需至少一位维护者确认
   PR must be confirmed by at least one maintainer before merging

ℹ️ 刷新CI状态操作需要具备仓库写入权限。
ℹ️ Refresh CI status operation requires repository Write permission.

[Rbb666]

这块有语法错误：

[BernardXiong]

还真是的。后面用drawio重新绘一份吧

[CXSforHPU]

flowchart TD
    ROM["BootROM/BL1<br/>QEMU 固件"]
    START["_start<br/>(entry_point.S)"]
    MMU["init_mmu_early<br/>enable_mmu_early"]
    CBOOT["rtthread_startup()"]
    BOARD["rt_hw_board_init<br/>-> rt_hw_common_setup"]
    MAIN["main_thread_entry"]
    PSCI["rt_hw_secondary_cpu_up<br/>(PSCI CPU_ON)"]
    SECASM["_secondary_cpu_entry<br/>(ASM)"]
    SECC["rt_hw_secondary_cpu_bsp_start"]
    SCHED["rt_system_scheduler_start"]
    RUN["多核调度运行态"]

    ROM --> START
    START --> MMU
    MMU --> CBOOT
    CBOOT --> BOARD
    BOARD --> MAIN
    MAIN --> PSCI
    PSCI --> SECASM
    SECASM --> SECC
    SECC --> SCHED
    SCHED --> RUN

Loading

这样修改后 ，显示图片的话，我这边测试是没有问题的