- we had `_DEBUG=n` forced, which conflicted with `_EXPERT=y`;
- some important SBC features (like _GPIO_SYSFS) depend on _EXPERT=y
- we've plans to enable BTF/CO-RE kernels soon, so removing the non-debug enforcement makes some sense
- also, .config's will be free to determine debug config, nothing's changing in those here
- remove the `_EMBEDDED` special case handling, we can do that as well now
- add a separate hook to renable `CONFIG_GPIO_SYSFS=y`; it was a victim of `EXPERT=n` in some kernels
- this does not include rewrites of all the .configs -- those should be done in a separate batch -- either way effect is the same, hooks will always override .config's
- during rewrites, a large number of new options will show up, since `_EXPERT=y` is used as dependency for many of Kernel's experimental-ish features
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