Amdgpu module is references even after unbinding the vtcon

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Hi Thomas,

we ran into a problem with the general fbcon/fbdev implementation and 
though that you might have some idea.

What happens is the following:
1. We load amdgpu and get our normal fbcon.
2. fbcon allocates a dump BO as backing store for the console.
3. GDM/X/Applications start, new framebuffers are created BOs imported, 
exported etc...
4. Somehow X or GDM iterated over all the framebuffer objects the 
kernels knows about and export them as DMA-buf.
5. Application/X/GDM are stopped, handles closed, framebuffers released 
etc...
6. We unbind vtcon.

At this point the amdgpu module usually has a reference count of 0 and 
can be unloaded, but since GDM/X/Whoever iterated over all the known 
framebuffers and exported them as DMA-buf (for whatever reason idk) we 
now still have an exported DMA-buf and with it a reference to the module.

Any idea how we could prevent that?

Thanks,
Christian.