KVM: x86: don't take kvm->irq_lock when creating IRQCHIP

I don't see any reason any more for this lock, seemed to be used to protect
removal of kvm->arch.vpic / kvm->arch.vioapic when already partially
inititalized, now access is properly protected using kvm->arch.irqchip_mode
and this shouldn't be necessary anymore.

Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>