kvm: require KVM_IRQFD for kernel irqchip

KVM_IRQFD was introduced in Linux 2.6.32, and since then it has always been
available on architectures that support an in-kernel interrupt controller.
We can require it unconditionally.

Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/riscv/kvm/kvm-cpu.c

@@ -1420,7 +1420,7 @@ void kvm_riscv_aia_create(MachineState *machine, uint64_t group_shift,
         exit(1);
     }
 
-    kvm_msi_via_irqfd_allowed = kvm_irqfds_enabled();
+    kvm_msi_via_irqfd_allowed = true;
 }
 
 static void kvm_cpu_instance_init(CPUState *cs)