nouveau: import libdrm_nouveau

Most of the code is copied as is, but there are a couple of changes:

• drop pre nvif code (which means we require at least linux 4.4 now)
• nouveau_list -> list_head
• pthread_mutex_t -> simple_mtx_t
• nvif_unwrap removed
• reworked object allocation UAPI calls (I really really don't like the current code and don't even want to have it inside the git history 🙃 )
• moved assignments out of if statements
• nouveau_object_mthd -> nouveau_device_info

Most of the reworked object allocation code was copied from NVK. There are a couple of other smaller changes, mostly removing dead code or making code a bit more straight forward to follow. I hope there are no regressions but this still needs to be tested on at least those GPU archs:

• nv30 (g73)
• nv50 (gt218)
• nvc0 (gf108)
• nve0 (gk208)
• gp100 (gp108)
• tu100 (tu102)

Things to still take care of:

• src/gallium/winsys/nouveau/drm/nouveau.c contains some UAPI bits missing from the kernel headers, those need to be added.

In a follow up merge requests I'm planning to support VM_BIND as this will be required to properly fix modifiers.