target/arm: Pass ARMCPU to aarch64_aa32_a57_init

There's no reason to pass Object when ARMCPU is more appropriate.

Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20260812204435.295067-3-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>