drm/i915: Gather all the power well->domain mappings to one place

Shuffle the power well->domain mapping macros around so they are at one
place in old->new GEN order.
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1499352040-8819-19-git-send-email-imre.deak@intel.comSigned-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>