[MR] etnaviv: Fold in etnaviv specific libdrm bits

[Guido Günther]

Hi,
(due to the size i've published this via a gitlab MR and since I'm not
sure everyone follow these as well):

Lucas suggested to fold the etnaviv part of libdrm into mesa as preparation for
softpin.  So here we go. I've been using this code quite a while now and just
polished it a bit for submission.
These changes were done over libdrm as of 922d92994267743266024ecceb734ce0ebbca808:

- Use mesa's ARRAY_SIZE
- Use mesa's atomic definitions
- Use mesa's os_map instead of drm_map
- Drop drm_{public,private}
- Rename table_lock to etna_drm_table_lock to avoid a conflict with freedreno's
  table_lock.
- Rename bo_del to _etna_drm_bo_del to avoid a conflict with freedreno's
- bo_del

https://gitlab.freedesktop.org/mesa/mesa/merge_requests/970

Cheers,
 -- Guido