moduledb is not updated when x11-drm-20060608 is emerged (haven't tried other versions). Thus, it is not automatically re-emerged by running sys-kernel/module-rebuild after upgrading the kernel.
Created attachment 93810 [details, diff] Call linux-mod_pkg_postinst to add x11-drm to moduledb This very simple patch should fix it. I learned how to do this from bug #130523.
Fixed in portage. Thanks.