hw/arm/armv7m: alias the NVIC "num-prio-bits" property

hw/arm/armv7m: alias the NVIC "num-prio-bits" property

A SoC will not have a direct access to the NVIC embedded in its ARM
core. By aliasing the "num-prio-bits" property similarly to what is
done for the "num-irq" one, a SoC can easily configure it on its
armv7m instance.

Signed-off-by: Samuel Tardieu <sam@rfc1149.net>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240106181503.1746200-3-sam@rfc1149.net
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>