drm/i915: move more defs in intel_display_power.h

Move over structures, enums and macros from intel_display.h and
i915_drv.h to have all the display PM defines in the same header.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190531222409.9177-3-daniele.ceraolospurio@intel.com