drm/i915/display: add I915 conditional build to intel_dvo.h

Add stubs for !I915.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/d43b27742297083b37d52222c4bb72b062ef4967.1694514689.git.jani.nikula@intel.com

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

@@ -8,6 +8,12 @@
 
 struct drm_i915_private;
 
+#ifdef I915
 void intel_dvo_init(struct drm_i915_private *dev_priv);
+#else
+static inline void intel_dvo_init(struct drm_i915_private *dev_priv)
+{
+}
+#endif
 
 #endif /* __INTEL_DVO_H__ */