[PATCH v2 0/4] mkimage: validate image references in FIT configurations

[Aristo Chen]

Hi all,

This series introduces a validation step in mkimage to ensure that all image
names referenced under the /configurations node of a FIT source (ITS) are
actually defined under the /images node.

### Motivation

When using mkimage to build FIT images, it's easy to mistakenly reference
nonexistent image nodes in configurations (e.g., referencing a missing `fdt` or
`firmware` node). Such issues are often not caught until runtime in U-Boot.

This series aims to catch these errors early during FIT image creation by
validating the configuration references in mkimage itself.

### Changes in v2

- Use `fdt_stringlist_count()` and `fdt_stringlist_get()` to handle stringlist properties cleanly
- Validate additional properties (`firmware`, `fpga`, `script`)
- Improve error messages by including the failing configuration and property name
- Refactor error propagation in `fit_handle_file()` as a separate commit
- Update all affected binman test DTS files to include the missing `atf` and `uboot` image nodes
- Add a new Python test case under `test/py/` to ensure mkimage correctly fails when an image is missing

Best regards,
Aristo Chen