target/arm/cpu64: Allow -host for nitro

The nitro accel does not actually make use of CPU emulation or details:
It always uses the host CPU regardless of configuration. Machines for
the nitro accel select the host CPU type as default to have a clear
statement of the above and to have a unified cpu type across all
supported architectures.

The arm64 logic on Linux currently only allows -cpu host for KVM based
virtual machines. Add a special case for nitro so that when the nitro
accel is active, it allows use of the host cpu type.

Signed-off-by: Alexander Graf <graf@amazon.com>
Link: https://lore.kernel.org/r/20260225220807.33092-8-graf@amazon.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/arm/cpu64.c

@@ -813,6 +813,14 @@ static void aarch64_a53_initfn(Object *obj)
 static void aarch64_host_initfn(Object *obj)
 {
     ARMCPU *cpu = ARM_CPU(obj);
+
+#if defined(CONFIG_NITRO)
+    if (nitro_enabled()) {
+        /* The nitro accel uses -cpu host, but does not actually consume it */
+        return;
+    }
+#endif
+
 #if defined(CONFIG_KVM)
     kvm_arm_set_cpu_features_from_host(cpu);
     aarch64_add_sve_properties(obj);