accel: Introduce accel_cpu_common_unrealize() stub

Prepare the stub for parity with accel_cpu_common_realize().

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20231003123026.99229-5-philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
3 files changed