drm/i915: reorganize intel_drv.h

Daniel complained that we keep adding stuff to the bottom of the file,
so we constantly have conflicts. So reorganize everything and split
them file-by-file, also sorting the files in alphabetical order. This
way, patches touching different files will have a smaller chance of
conflicting. Of course, this commit will conflict with everybody on
the list :)

Also remove a few useless comments and make some things fit into 80
lines.

v2: - Conflict with intel_ddi_get_config
Requested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>