Allow ttm_buffer_object without resource

[Christian König]

Am 29.03.22 um 16:02 schrieb Daniel Vetter:
> On Tue, Mar 29, 2022 at 01:02:32PM +0200, Christian König wrote:
>> Hi guys,
>>
>> this patch set cleans up the handling of TTM buffer objects quite a bit
>> by allowing to create them without allocating a ttm_resource as well.
>>
>> That's not only cleaner in general, but also a necessary prerequisite for
>> quite a number of related work.
> Maybe there's some threads I missed, but I can't really guess what this
> could be useful for without even a hint.

Well about a week ago Bob send me a partial implementation of this and 
said he needs it for i915. What exactly i915 needs here I'm not sure 
about either.

I have this cleanup in the pipeline because amdgpu wants to improve his 
page table handling with this and independent of those driver use case 
patches #10 and #11 drop allocating dummy resources for two use cases in 
TTM.

Christian.

> -Daniel