drm/radeon: fixup tiling group size and backendmap on r6xx-r9xx (v4)

Tiling group size is always 256bits on r6xx/r7xx/r8xx/9xx. Also fix and
simplify render backend map. This now properly sets up the backend map
on r6xx-9xx which should improve 3D performance.

Vadim benchmarked also:
Some benchmarks on juniper (5750), fullscreen 1920x1080,
first result - kernel 3.4.0+ (fb21affa), second - with these patches:

Lightsmark:   91 fps => 123 fps    +35%
Doom3:        74 fps => 101 fps    +36%

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
index 492654f..e25836b 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -1845,6 +1845,11 @@
 extern void r600_hdmi_enable(struct drm_encoder *encoder);
 extern void r600_hdmi_disable(struct drm_encoder *encoder);
 extern void r600_hdmi_setmode(struct drm_encoder *encoder, struct drm_display_mode *mode);
+extern u32 r6xx_remap_render_backend(struct radeon_device *rdev,
+				     u32 tiling_pipe_num,
+				     u32 max_rb_num,
+				     u32 total_max_rb_num,
+				     u32 enabled_rb_mask);
 
 /*
  * evergreen functions used by radeon_encoder.c