drm/radeon/kms: allocate vram scratch page on 6xx+

The vram scratch was originally only used on some 7xx asics
to work around a hw bug.  Allocate the scratch page on all 6xx+
radeons and set the MC_VM_SYSTEM_APERTURE_DEFAULT_ADDR to point
to it.  We shouldn't ever hit it since we limit the system
aperture to vram or vram and AGP, but better safe than sorry.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/evergreen.c

@@ -3031,6 +3031,10 @@ static int evergreen_startup(struct radeon_device *rdev)
 		}
 	}
 
+	r = r600_vram_scratch_init(rdev);
+	if (r)
+		return r;
+
 	evergreen_mc_program(rdev);
 	if (rdev->flags & RADEON_IS_AGP) {
 		evergreen_agp_enable(rdev);
@@ -3235,6 +3239,7 @@ void evergreen_fini(struct radeon_device *rdev)
 	radeon_ib_pool_fini(rdev);
 	radeon_irq_kms_fini(rdev);
 	evergreen_pcie_gart_fini(rdev);
+	r600_vram_scratch_fini(rdev);
 	radeon_gem_fini(rdev);
 	radeon_fence_driver_fini(rdev);
 	radeon_agp_fini(rdev);