[Intel-gfx] Rework DRM proc file handling [rev 2]

[Ben Gamari]

This is the latest patch series reworking the drm proc file handling
using seq_file. Like before, I've moved some of the debug-oriented proc
files into debugfs, especially those pertaining to i915. Moreover, the
series now has a proper git history and is split up better than the
previous behemouth. 

Still, I have yet to get batch buffer dumping
working, but it should nevertheless be stable. Let me know how it looks.
I corrected a bunch of whitespace issues so it should be mergeable (or
at least close). I'll be looking forward to hearing comments. Thanks,

  - Ben