v2025.10 env Kconfig rename (fb5235239aad) removed backward compatibility

[Ozan Durgut]

Dear U-Boot maintainers,

I hope you're doing well.

I would like to raise a backward compatibility concern regarding commit 
fb5235239aad ("env: Rename DEFAULT_ENV_FILE to 
ENV_DEFAULT_ENV_TEXT_FILE"), which landed in the v2025.10 release.

Previously used Kconfig symbols CONFIG_USE_DEFAULT_ENV_FILE and 
CONFIG_DEFAULT_ENV_FILE have been replaced with 
CONFIG_ENV_USE_DEFAULT_ENV_TEXT_FILE and 
CONFIG_ENV_DEFAULT_ENV_TEXT_FILE. However, the old symbols were removed 
outright, without a compatibility shim or deprecation period.

This change causes breakage when integrating U-Boot with Buildroot, as 
Buildroot currently lacks a mechanism to handle such changes 
conditionally based on U-Boot's version. As a result, downstream users 
are forced to choose between breaking support for older or newer U-Boot 
versions.

Would it be possible to consider introducing the legacy symbols as 
aliases, or at least providing a transitional method to support both? If 
there is a preferred approach to handle such transitions, or if you 
would recommend a specific pattern, we would be happy to align with 
upstream direction.

Looking forward to your input.

Best regards,
Ozan Durgut
Analog Devices