hw/intc/loongarch_extioi: Add dynamic cpu number support

hw/intc/loongarch_extioi: Add dynamic cpu number support

On LoongArch physical machine, one extioi interrupt controller only
supports 4 cpus. With processor more than 4 cpus, there are multiple
extioi interrupt controllers; if interrupts need to be routed to
other cpus, they are forwarded from extioi node0 to other extioi nodes.

On virt machine model, there is simple extioi interrupt device model.
All cpus can access register of extioi interrupt controller, however
interrupt can only be route to 4 vcpu for compatible with old kernel.

This patch adds dynamic cpu number support about extioi interrupt.
With old kernel legacy extioi model is used, however kernel can detect
and choose new route method in future, so that interrupt can be routed to
all vcpus.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20231215100333.3933632-4-maobibo@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>