drm/i915: Use intel_ types in intel_atomic_check()

Switch to using intel_ types instead of drm_ types. Avoids
ugly casts and nasty aliasing variables with different types.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190517193132.8140-9-ville.syrjala@linux.intel.com


Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>