drm/i915: Throw out WIP CHV power well definitions

Expecting CHV power wells to be just an extended versions of the VLV
power wells, a bunch of commented out power wells were added in
anticipation when Punit folks would implement it all. Turns out they
never did, and instead CHV has fewer power wells than VLV. Rip out all
the #if 0'ed junk that's not needed.

v2: Rename the "pipe-a" well to "display" to match VLV
    Clarify the pipe A power well relationship to pipes B and C (Deepak)

Reviewed-by: Deepak S <deepak.s@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>