Port the i915 HDMI infoframe code to the common infrastructure v2

[Damien Lespiau]

Re-posting the whole series because I forgot dri-devel in the first version and
also added a few patches from the review.

Version 2 of the series:
  http://lists.freedesktop.org/archives/intel-gfx/2013-August/031183.html

With Ville's comments so far addressed.

I've also added the already posted drm patch:
  http://lists.freedesktop.org/archives/dri-devel/2013-August/042900.html
in this version as we depend on it to not generate invalid infoframe after
having ported i915 to the generic helpers.

-- 
Damien