LoongArch: KVM: Add stat information with kernel irqchip

Move stat information about kernel irqchip from VM to vCPU, since all
vm exiting events should be vCPU relative. And also add entry with
structure kvm_vcpu_stats_desc[], so that it can display with directory
/sys/kernel/debug/kvm.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>