drm/i915/display: add I915 conditional build to vlv_dsi.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/9f538824f15096b0c1444ee50d175a0a22d7bd5e.1694514689.git.jani.nikula@intel.com

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

@@ -12,8 +12,21 @@ enum port;
 struct drm_i915_private;
 struct intel_dsi;
 
+#ifdef I915
 void vlv_dsi_wait_for_fifo_empty(struct intel_dsi *intel_dsi, enum port port);
 enum mipi_dsi_pixel_format pixel_format_from_register_bits(u32 fmt);
 void vlv_dsi_init(struct drm_i915_private *dev_priv);
+#else
+static inline void vlv_dsi_wait_for_fifo_empty(struct intel_dsi *intel_dsi, enum port port)
+{
+}
+static inline enum mipi_dsi_pixel_format pixel_format_from_register_bits(u32 fmt)
+{
+	return 0;
+}
+static inline void vlv_dsi_init(struct drm_i915_private *dev_priv)
+{
+}
+#endif
 
 #endif /* __VLV_DSI_H__ */