[security][mbedtls] add support for loading certificates from the file system

[Evlers]

RT-Thread-packages/mbedtls#61

[Copilot]

Pull request overview

This PR updates the RT-Thread package index entry for security/mbedtls to expose a new Kconfig option for loading CA certificates from a filesystem directory, aligning the package configuration with upstream support.

Changes:

• Add PKG_USING_MBEDTLS_CERTS_FROM_FS menuconfig option to enable loading CA certs from a directory.
• Add PKG_MBEDTLS_CERTS_DIR string config to set the certificate directory path (default /romfs/certs).
• Hide the “Select Root Certificate” menu when filesystem-based cert loading is enabled.

[Copilot]

[operational_implications/运行影响]: Selecting ROMFS conflicts with “filesystem directory” behavior / 选择 ROMFS 与“文件系统目录”行为不一致

English: PKG_USING_MBEDTLS_CERTS_FROM_FS currently select RT_USING_DFS_ROMFS, but the option/help and examples imply certificates can be loaded from an arbitrary runtime filesystem directory (e.g. /data/certs). Forcing ROMFS may enable an unnecessary filesystem backend and is inconsistent with non-ROMFS paths. Consider depending on/selecting the generic file/dir APIs actually required (e.g. RT_USING_POSIX_FS/DFS) and keep ROMFS as just the default path example rather than a hard requirement.
中文：PKG_USING_MBEDTLS_CERTS_FROM_FS 目前通过 select RT_USING_DFS_ROMFS 强制启用 ROMFS，但选项说明与示例表明证书目录可能来自任意运行时文件系统（例如 /data/certs）。强制 ROMFS 可能引入不必要的文件系统后端，并与非 ROMFS 路径不一致。建议改为依赖/选择实际需要的通用文件/目录接口（如 RT_USING_POSIX_FS/DFS），ROMFS 仅作为默认路径示例而非硬性依赖。

Suggested change

select RT_USING_DFS_ROMFS

[Copilot]

[spelling/拼写与措辞]: Grammar in prompt string / 选项提示语法不完整

English: The prompt text "Load CA certificates from filesystem directory" is missing an article and reads awkwardly. Consider changing it to "Load CA certificates from a filesystem directory" (or "from the filesystem").
中文：提示语 "Load CA certificates from filesystem directory" 缺少冠词，语句不够通顺。建议改为 "Load CA certificates from a filesystem directory"（或 "from the filesystem"）。

Suggested change

	bool "Load CA certificates from filesystem directory"
	bool "Load CA certificates from a filesystem directory"

[Copilot]

[discrepancy_with_pr_description/PR 描述]: PR description is only a link / PR 描述仅包含链接

English: The PR description only links to an upstream PR and doesn’t summarize What/Why/How for this repository change (e.g., which Kconfig symbols are added and why). Please add a brief description and list the modified file(s) to make review and future archaeology easier.
中文：PR 描述仅提供了上游 PR 链接，没有说明本仓库的变更内容与动机（What/Why/How，例如新增了哪些 Kconfig 符号、目的是什么）。建议补充简要说明并列出修改文件，便于评审与后续追溯。