drm/radeon: fill in rb backend map on evergreen/ni.

This looks to have never gotten filled in, and it seems to
 trigger a bug in mesa.
Reviewed-by: NRoland Scheidegger <sroland@vmware.com>
Reported-by: NRoland Scheidegger <sroland@vmware.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/evergreen.c

@@ -3513,6 +3513,7 @@ static void evergreen_gpu_init(struct radeon_device *rdev)
 		tmp = r6xx_remap_render_backend(rdev, tmp, rdev->config.evergreen.max_backends,
 						EVERGREEN_MAX_BACKENDS, disabled_rb_mask);
 	}
+	rdev->config.evergreen.backend_map = tmp;
 	WREG32(GB_BACKEND_MAP, tmp);
 
 	WREG32(CGTS_SYS_TCC_DISABLE, 0);

drivers/gpu/drm/radeon/ni.c

@@ -1148,6 +1148,7 @@ static void cayman_gpu_init(struct radeon_device *rdev)
 						rdev->config.cayman.max_shader_engines,
 						CAYMAN_MAX_BACKENDS, disabled_rb_mask);
 	}
+	rdev->config.cayman.backend_map = tmp;
 	WREG32(GB_BACKEND_MAP, tmp);
 
 	cgts_tcc_disable = 0xffff0000;