drm/i915/hdmi: convert to struct intel_display

Going forward, struct intel_display shall replace struct
drm_i915_private as the main display device data pointer type. Convert
intel_hdmi.[ch] to struct intel_display. Remove intel_hdmi_to_i915().

Some stragglers are left behind where needed.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/fa74b67935eb7e8084f57688a9683a36cb1d1a4c.1725012870.git.jani.nikula@intel.com

drivers/gpu/drm/i915/display/intel_hdmi.h

@@ -58,6 +58,5 @@ int intel_hdmi_dsc_get_num_slices(const struct intel_crtc_state *crtc_state,
 				  int src_max_slices, int src_max_slice_width,
 				  int hdmi_max_slices, int hdmi_throughput);
 int intel_hdmi_dsc_get_slice_height(int vactive);
-struct drm_i915_private *intel_hdmi_to_i915(struct intel_hdmi *intel_hdmi);
 
 #endif /* __INTEL_HDMI_H__ */