drm/i915: Switch fbc over to for_each_new_intel_plane_in_state()

Stop using the old for_each_intel_plane_in_state() type iteration
macro and replace it with for_each_new_intel_plane_in_state().
And similarly replace drm_atomic_get_existing_crtc_state() with
intel_atomic_get_new_crtc_state(). Switch over to intel_ types
as well to make the code less cluttered.

v2: s/plane/i9xx_plane/ etc. (James)

Cc: James Ausmus <james.ausmus@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171117191917.11506-8-ville.syrjala@linux.intel.com


Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>