drm/i915: Reinit display irqs and hpd from chv pipe-a power well

On chv the pipe-a power well is the new disp2d well, and it kills pretty
much everything in the display block. So we need to do the the same
dance that vlv does wrt. display irqs and hpd when the power well goes
up or down.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>