drm/i915/display: move to_intel_frontbuffer to header

This will be used for some refactoring in other files, so move it
first.
Signed-off-by: Dave Airlie <airlied@redhat.com>
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/20201221090449.8288-2-jani.nikula@intel.com

drivers/gpu/drm/i915/display/intel_display.c

@@ -3611,12 +3611,6 @@ static void intel_plane_disable_noatomic(struct intel_crtc *crtc,
 	intel_disable_plane(plane, crtc_state);
 }
 
-static struct intel_frontbuffer *
-to_intel_frontbuffer(struct drm_framebuffer *fb)
-{
-	return fb ? to_intel_framebuffer(fb)->frontbuffer : NULL;
-}
-
 static void
 intel_find_initial_plane_obj(struct intel_crtc *intel_crtc,
 			     struct intel_initial_plane_config *plane_config)

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

@@ -1805,4 +1805,10 @@ static inline u32 intel_plane_ggtt_offset(const struct intel_plane_state *state)
 	return i915_ggtt_offset(state->vma);
 }
 
+static inline struct intel_frontbuffer *
+to_intel_frontbuffer(struct drm_framebuffer *fb)
+{
+	return fb ? to_intel_framebuffer(fb)->frontbuffer : NULL;
+}
+
 #endif /*  __INTEL_DISPLAY_TYPES_H__ */