添加了NXP MCXA346的UART demo

[tm456-43]

拉取/合并请求描述：(PR description)

[

为什么提交这份PR (why to submit this PR)

NXPFRDM-MCXA346评测活动

你的解决方案是什么 (what is your solution)

添加UART3的驱动，完成esp8266的联网测试

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

• BSP:bsp\nxp\mcx\mcxa\frdm-mcxa346

• .config:
  CONFIG_RT_USING_SYSTEM_WORKQUEUE=y
  CONFIG_RT_USING_SAL=y
  CONFIG_RT_USING_AT=y
  CONFIG_PKG_USING_AT_DEVICE=y

• action:
  https://github.com/tm456-43/rt-thread/actions/runs/20706764588

]

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

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[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）。
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完成后，提交将自动更新至 NXP_FRDM-MCXA346_UART_demo 分支，关联的 Pull Request 也会同步更新。
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[github-actions]

📌 Code Review Assignment

🏷️ Tag: bsp_mcxa

Reviewers: @hywing

Changed Files (Click to expand)

• bsp/nxp/mcx/mcxa/frdm-mcxa346/.config
• bsp/nxp/mcx/mcxa/frdm-mcxa346/applications/at_sample_client.c
• bsp/nxp/mcx/mcxa/frdm-mcxa346/applications/uart3_test.c
• bsp/nxp/mcx/mcxa/frdm-mcxa346/applications/uart_sample.c
• bsp/nxp/mcx/mcxa/frdm-mcxa346/board/MCUX_Config/board/pin_mux.c
• bsp/nxp/mcx/mcxa/frdm-mcxa346/project.uvoptx
• bsp/nxp/mcx/mcxa/frdm-mcxa346/project.uvprojx
• bsp/nxp/mcx/mcxa/frdm-mcxa346/rtconfig.h

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📊 Current Review Status (Last Updated: 2026-01-05 14:16 CST)

• ⌛ @hywing Pending Review

---

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ℹ️ Refresh CI status operation requires repository Write permission.

[Rbb666]

注释部分编码不对

[Rbb666]

保留最小即可，不需要添加这么多依赖

[Rbb666]

有冲突需要解决下

[kurisaW]

测评demo不建议提交上来，当然你可以优化一下，做成一个demo，通过在board/kconfig下添加一个宏定义配置项，相关源文件放到board/port/at_xxx/目录下，另外.config和rtconfig.h不建议被修改（默认保持工程的最小体量）

[Rbb666]

demo的话需要参考下面的方式，对接到utest框架：

https://github.com/RT-Thread/rt-thread/tree/master/bsp/k230/drivers/utest