Added some boilerplate for the structs, documented members where they
are relevant and plenty of markup for hyperlinks all over. And a few
small wording polish.

Note that the intro needs some more love after the DRM_MM_INSERT_*
patch from Chris has landed.

v2: Spelling fixes (Chris).

v3: Use &struct foo instead of &foo structure (Chris).

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: NDavid Herrmann <dh.herrmann@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1483044517-5770-3-git-send-email-daniel.vetter@ffwll.ch

ttm_global_reference was renamed to drm_global_reference.  This updates
the documentation to reflect that.  While we are there, document the
drm_global_reference API and update the initialization interface
documentation.
Signed-off-by: NGabriel Krisman Bertazi <krisman@collabora.co.uk>
[danvet: Keep the warning, ttm docs are still massively inadequate.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161228143216.26821-7-krisman@collabora.co.uk

Now that we don't have automatic syntax highlighting, use the code-block
directive with the explicitly selected language, where appropriate.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>

- Readjust headings - we lost one level through the extraction into a
  separate .rst file.
- Merge helper reference sections with the helper documentation - that
  split was just an artifact of the docbook toolchain sucking at too
  deep nesting levels. No such problems with sphinx.
- Move the cma helpers in with the gem documentation, since they're
  helpers to implement gem using CMA/dma memory as a backend.
Reviewed-by: NSean Paul <seanpaul@chromium.org>
Signed-off-by: NDaniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471034937-651-4-git-send-email-daniel.vetter@ffwll.ch

Make the documents more manageable.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/be992e56eb8442d6e03b52444df5a42525085718.1466506505.git.jani.nikula@intel.com