drm/i915: Support for Cougarpoint PCH display pipeline

Cougarpoint is the new PCH for Sandybridge CPU. This one resolves the
chipset change for display pipeline compared to previous Ibexpeak PCH.

Sandybridge/Cougarpoint has different FDI training parameters, so this also
makes seperate FDI training functions for IBX and CPT. Other change includes
new transcoder DPLL select function to set which DPLL for transcoder to pick
up.

And with another new transcoder C introduced in Cougarpoint, each connector
has new transcoder select bits. This one adds that change to light up VGA.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>