drm: Add headers, stubs and constants required by Linux 4.10 code

drm: Define struct page and use it everywhere

* Removing countless differences with Linux

* struct page is essentially struct vm_page named differently.
Both can be casted to the other one withou

drm: Define struct page and use it everywhere

* Removing countless differences with Linux

* struct page is essentially struct vm_page named differently.
Both can be casted to the other one without further thought.

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