drm/i915: make pool objects read-only

For our current users we don't expect pool objects to be writable from
the gpu.
Signed-off-by: NMatthew Auld <matthew.auld@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Fixes: 4f7af194 ("drm/i915: Support ro ppgtt mapped cmdparser shadow buffers")
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191119150154.18249-1-matthew.auld@intel.com
(cherry picked from commit d18580b0)
Signed-off-by: NRodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/i915/gt/intel_engine_pool.c

@@ -103,6 +103,8 @@ node_create(struct intel_engine_pool *pool, size_t sz)
 		return ERR_CAST(obj);
 	}
 
+	i915_gem_object_set_readonly(obj);
+
 	node->obj = obj;
 	return node;
 }