[Intel-gfx] Sandybridge/Cougarpoint display enabling

[Zhenyu Wang]

This series is for Sandybridge/Cougarpoint display output enabling.
Cougarpoint will be the new PCH for Sandybridge CPU.

This is tested on a mobile platform, regression test has been made
on Ironlake platform and also Sandybridge/Ibexpeak system.

Commits are also available on 'sandybridge' branch of my drm-intel
tree, http://cgit.freedesktop.org/~zhen/drm-intel/log/?h=sandybridge
and based on recent 'encoder-rework' branch.

thanks.