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

Add stubs for !I915. Not all the functions need to be stubbed.
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/930c8d332d425a54dae7af16aed26ec293f80afd.1694514689.git.jani.nikula@intel.com

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

@@ -32,7 +32,16 @@ u32 bxt_dsi_get_pclk(struct intel_encoder *encoder,
 		     struct intel_crtc_state *config);
 void bxt_dsi_reset_clocks(struct intel_encoder *encoder, enum port port);
 
+#ifdef I915
 void assert_dsi_pll_enabled(struct drm_i915_private *i915);
 void assert_dsi_pll_disabled(struct drm_i915_private *i915);
+#else
+static inline void assert_dsi_pll_enabled(struct drm_i915_private *i915)
+{
+}
+static inline void assert_dsi_pll_disabled(struct drm_i915_private *i915)
+{
+}
+#endif
 
 #endif /* __VLV_DSI_PLL_H__ */