drm/i915: adjust sprite base address

Just like in:

commit c2c75131244507c93f812862fdbd4f3a37139401
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Thu Jul 5 12:17:30 2012 +0200

    drm/i915: adjust framebuffer base address on gen4+

but this time, for the sprite planes. This ensures that the
sprite offset are always inside the supported hardware limits since it
becomes the offset into a page and we adjust the base address to a page
boundary.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 8839ed5..5b0b22a 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -585,6 +585,10 @@
 extern void intel_update_linetime_watermarks(struct drm_device *dev, int pipe,
 			 struct drm_display_mode *mode);
 
+extern unsigned long intel_gen4_compute_offset_xtiled(int *x, int *y,
+						      unsigned int bpp,
+						      unsigned int pitch);
+
 extern int intel_sprite_set_colorkey(struct drm_device *dev, void *data,
 				     struct drm_file *file_priv);
 extern int intel_sprite_get_colorkey(struct drm_device *dev, void *data,