drm/i915: Pass proper old/new states to intel_plane_atomic_check_with_state()

drm/i915: Pass proper old/new states to intel_plane_atomic_check_with_state()

Eliminate plane->state and crtc->state usage from
intel_plane_atomic_check_with_state() and its callers. Instead pass the
proper states in or dig them up from the top level atomic state.

Note that intel_plane_atomic_check_with_state() itself isn't allowed to
use the top level atomic state as there is none when it gets called from
the legacy cursor short circuit path.

v2: Rename some variables for easier comprehension (Maarten)

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170823152226.22938-4-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>