kvm: introduce kvm_kernel_irqchip_* functions

The KVMState struct is opaque, so provide accessors for the fields
that will be moved from current_machine to the accelerator.  For now
they just forward to the machine object, but this will change.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/target/mips/kvm.c b/target/mips/kvm.c
index 578bc14..de3e26e 100644
--- a/target/mips/kvm.c
+++ b/target/mips/kvm.c
@@ -57,7 +57,7 @@
     return 0;
 }
 
-int kvm_arch_irqchip_create(MachineState *ms, KVMState *s)
+int kvm_arch_irqchip_create(KVMState *s)
 {
     return 0;
 }