LoongArch: KVM: Use standard bitops API with eiointc

Standard bitops APIs such test_bit() is used here, rather than manually
calculating the offset and mask. Also use non-atomic API __set_bit() and
__clear_bit() rather than set_bit() and clear_bit(), since the global
spinlock is held already.

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