drm/i915: Convert intel_crtc.c to struct intel_display

struct intel_display will replace struct drm_i915_private as
the main thing for display code. Convert intel_crtc.c code to
use it.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250206185533.32306-5-ville.syrjala@linux.intel.com