Expose qemu_cpu_list_lock globally so that we can use
WITH_QEMU_LOCK_GUARD and QEMU_LOCK_GUARD to simplify a few code paths
now and in future.

Signed-off-by: Jamie Iles <quic_jiles@quicinc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230427020925.51003-2-quic_jiles@quicinc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>