drm/i915: Add chv_power_wells[]

Add chv_power_wells[] so we can start to build up the power well support
for chv. Just the "always on" well there initialy.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Rafael Barbalho <rafael.barbalho@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>