drm/i915/chv: Add basic PM interrupt support for CHV

Enabled PM interrupt programming for CHV. Re-using gen8 code and extending same for CHV.

Signed-off-by: Deepak S <deepak.s@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>