drm/i915/display: add I915 conditional build to i9xx_wm.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/bf15b14d3d060fdb256c78d4b8514d642a8958e6.1694514689.git.jani.nikula@intel.com

drivers/gpu/drm/i915/display/i9xx_wm.h

@@ -12,9 +12,26 @@ struct drm_i915_private;
 struct intel_crtc_state;
 struct intel_plane_state;
 
+#ifdef I915
 bool ilk_disable_lp_wm(struct drm_i915_private *i915);
 void ilk_wm_sanitize(struct drm_i915_private *i915);
 bool intel_set_memory_cxsr(struct drm_i915_private *i915, bool enable);
 void i9xx_wm_init(struct drm_i915_private *i915);
+#else
+static inline bool ilk_disable_lp_wm(struct drm_i915_private *i915)
+{
+	return false;
+}
+static inline void ilk_wm_sanitize(struct drm_i915_private *i915)
+{
+}
+static inline bool intel_set_memory_cxsr(struct drm_i915_private *i915, bool enable)
+{
+	return false;
+}
+static inline void i9xx_wm_init(struct drm_i915_private *i915)
+{
+}
+#endif
 
 #endif /* __I9XX_WM_H__ */