build fix: CONFIG_DRM_I915=y && CONFIG_ACPI=n

drivers/gpu/drm/i915/i915_opregion.c:340: error: implicit declaration of function ‘register_acpi_notifier’
drivers/gpu/drm/i915/i915_opregion.c:361: error: implicit declaration of function ‘unregister_acpi_notifier’

Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/i915/Makefile

@@ -3,13 +3,14 @@
 # Direct Rendering Infrastructure (DRI) in XFree86 4.1.0 and higher.
 
 ccflags-y := -Iinclude/drm
-i915-y := i915_drv.o i915_dma.o i915_irq.o i915_mem.o i915_opregion.o \
+i915-y := i915_drv.o i915_dma.o i915_irq.o i915_mem.o \
           i915_suspend.o \
 	  i915_gem.o \
 	  i915_gem_debug.o \
 	  i915_gem_proc.o \
 	  i915_gem_tiling.o
 
+i915-$(CONFIG_ACPI)	+= i915_opregion.o
 i915-$(CONFIG_COMPAT)   += i915_ioc32.o
 
 obj-$(CONFIG_DRM_I915)  += i915.o

drivers/gpu/drm/i915/i915_drv.h

@@ -539,11 +539,18 @@ extern int i915_restore_state(struct drm_device *dev);
 extern int i915_save_state(struct drm_device *dev);
 extern int i915_restore_state(struct drm_device *dev);
 
+#ifdef CONFIG_ACPI
 /* i915_opregion.c */
 extern int intel_opregion_init(struct drm_device *dev);
 extern void intel_opregion_free(struct drm_device *dev);
 extern void opregion_asle_intr(struct drm_device *dev);
 extern void opregion_enable_asle(struct drm_device *dev);
+#else
+static inline int intel_opregion_init(struct drm_device *dev) { return 0; }
+static inline void intel_opregion_free(struct drm_device *dev) { return; }
+static inline void opregion_asle_intr(struct drm_device *dev) { return; }
+static inline void opregion_enable_asle(struct drm_device *dev) { return; }
+#endif
 
 /**
  * Lock test for when it's just for synchronization of ring access.