drm/i915: s/pipe_config/crtc_state/ in intel_crtc_atomic_check()

Clean up the mess with the drm vs. intel types in
intel_crtc_atomic_check() and rename varibles accordingly.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190913193157.9556-5-ville.syrjala@linux.intel.com