LoongArch: KVM: Add missing slots_lock for device register/unregister

LoongArch: KVM: Add missing slots_lock for device register/unregister

kvm_io_bus_register_dev() and kvm_io_bus_unregister_dev() should be
called under kvm->slots_lock. The unregister calls in ipi.c, eiointc.c
and pch_pic.c were also missing this protection. Add it to match the
register side.

Cc: stable@vger.kernel.org
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>