drm: Convert proc files to seq_file and introduce debugfs

The old mechanism to formatting proc files is extremely ugly. The
seq_file API was designed specifically for cases like this and greatly
simplifies the process.

Also, most of the files in /proc really don't belong there. This patch
introduces the infrastructure for putting these into debugfs and exposes
all of the proc files in debugfs as well.

This contains the i915 hooks rewrite as well, to make bisectability better.

Signed-off-by: Ben Gamari <bgamari@gmail.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>