drm/i915: framebuffer compression for GM45+

Add support for framebuffer compression on GM45 and above.  Removes
some unnecessary I915_HAS_FBC checks as well (this is now part of the
FBC display function).

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_drv.h

@@ -827,6 +827,7 @@ static inline void opregion_enable_asle(struct drm_device *dev) { return; }
 extern void intel_modeset_init(struct drm_device *dev);
 extern void intel_modeset_cleanup(struct drm_device *dev);
 extern void i8xx_disable_fbc(struct drm_device *dev);
+extern void g4x_disable_fbc(struct drm_device *dev);
 
 /**
  * Lock test for when it's just for synchronization of ring access.