Constify vmstate_ecc_state and vmstate_x86_cpu.

Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210408140706.23412-1-zhukeqian1@huawei.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>