I asked on the U-Boot mailing list for more information on this issue. The response from Tom Rini of Konsulko:
So, I mentioned this in the patch that migrated the option to Kconfig and marked it deprecated, and I plan to mention it in the release notes on Monday. But, this option has no in-tree users and I plan to remove the code in the near term, if no one with the relevant background steps up to re-implement it. Thanks!