accel-cpu: make cpu_realizefn return a bool

accel-cpu: make cpu_realizefn return a bool

overall, all devices' realize functions take an Error **errp, but return void.

hw/core/qdev.c code, which realizes devices, therefore does:

local_err = NULL;
dc->realize(dev, &local_err);
if (local_err != NULL) {
    goto fail;
}

However, we can improve at least accel_cpu to return a meaningful bool value.

Signed-off-by: Claudio Fontana <cfontana@suse.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210322132800.7470-9-cfontana@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>