drm/i915/display: add I915 conditional build to g4x_dp.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/ba92fc1dee1f71018179dbe10b91982c9c93e7e6.1694514689.git.jani.nikula@intel.com

drivers/gpu/drm/i915/display/g4x_dp.h

@@ -17,6 +17,7 @@ struct intel_crtc_state;
 struct intel_dp;
 struct intel_encoder;
 
+#ifdef I915
 const struct dpll *vlv_get_dpll(struct drm_i915_private *i915);
 enum pipe vlv_active_pipe(struct intel_dp *intel_dp);
 void g4x_dp_set_clock(struct intel_encoder *encoder,
@@ -26,5 +27,30 @@ bool g4x_dp_port_enabled(struct drm_i915_private *dev_priv,
 			 enum pipe *pipe);
 bool g4x_dp_init(struct drm_i915_private *dev_priv,
 		 i915_reg_t output_reg, enum port port);
+#else
+static inline const struct dpll *vlv_get_dpll(struct drm_i915_private *i915)
+{
+	return NULL;
+}
+static inline int vlv_active_pipe(struct intel_dp *intel_dp)
+{
+	return 0;
+}
+static inline void g4x_dp_set_clock(struct intel_encoder *encoder,
+				    struct intel_crtc_state *pipe_config)
+{
+}
+static inline bool g4x_dp_port_enabled(struct drm_i915_private *dev_priv,
+				       i915_reg_t dp_reg, int port,
+				       enum pipe *pipe)
+{
+	return false;
+}
+static inline bool g4x_dp_init(struct drm_i915_private *dev_priv,
+			       i915_reg_t output_reg, int port)
+{
+	return false;
+}
+#endif
 
 #endif