You can take BSD-licensed code and package it into a GPL bundle, which is what the kernel is doing. You can also extract the BSD-licensed code without the GPL-licensed code and it will be fine.
If Linux DRM weren't licensed under more permissive terms, OpenBSD simply wouldn't permit its inclusion.
When I compile my GPL code with a copy of somebody else's MIT code into a binary (shared address space), other people's copy of that MIT code is still MIT licensed.
Clearly two different files don't share the same address space. So no problem.