LoongArch: KVM: Implement vcpu interrupt operations

Implement vcpu interrupt operations such as vcpu set irq and vcpu
clear irq, using set_gcsr_estat() to set irq which is parsed by the
irq bitmap.

Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Tested-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Tianrui Zhao <zhaotianrui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>