at91 - support going forward

[Goetz Goerisch]

Dear all,

The at91 target has an open PR for testing kernel 6.12 for many months.

https://github.com/openwrt/openwrt/pull/19471

Also the discussion is ongoing in the forum:
https://forum.openwrt.org/t/kernel-6-12-at91-target-needs-basic-testing-and-debugging-or-it-will-be-dropped/242857

So far no one has taken up the ball to test this target.
I typically rebase after a kernel bump and run a build test, but have
no target to test.

Please decide how to proceed.

Cheers Goetz