hvf: arm: allow exposing minimal PMU for kernel-irqchip=on

When running with the Apple vGIC, a minimum PMU is exposed by Hypervisor.framework
if a valid PMUVer register value is set. That PMU isn't exposed otherwise.

Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20260429190532.26538-9-mohamed@unpredictable.fr
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>