llvmpipe: warn about illegal use of objects in different contexts

llvmpipe: warn about illegal use of objects in different contexts

Doing that is clearly a bug. We can't quite assert as st/mesa may hit this,
but increase at least visibility of it a bit.
(For the non-refcounted objects it would be illegal too, but we can't detect
that unless we'd store the context ourselves. Plus, those don't tend to cause
random crashes at context or object destruction time... So just sampler views,
surfaces and so targets for now.)

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>