vmm: acpi: provide FADT PM1a event/control blocks for nested Hyper-V

A Windows guest that launches nested Hyper-V (for example to run WSL2)
fails to start its hypervisor on cloud-hypervisor's HW-reduced-ACPI
FADT. hvloader's hypervisor-launch path (0x18000f01c -> 0x180015628 ->
0x180015788) registers every legacy PM register block via 0x1800158dc
and rejects any block whose GAS address is 0 with status 8
(STATUS_INVALID_DEVICE_REQUEST). hvix64 then never launches and
HypervisorPresent stays False. The HW-reduced FADT leaves those blocks
zero.

Emit valid PM1a event/control blocks (I/O ports, lengths and X_GAS) in
the FADT and reserve those ports in the I/O allocator so nothing else
claims them. The HW-reduced guest OS ignores the legacy ports; only
hvloader's ACPI validation reads them.

These blocks are only useful to a guest that itself runs an enlightened
hypervisor, so emit them only when both guest nesting and the Hyper-V
enlightenments are enabled (--cpu nested=on,kvm_hyperv=on).

Signed-off-by: doge <me@crackerben.com>

vmm/src/cpu.rs

@@ -1089,6 +1089,16 @@ impl CpuManager {
         Ok(())
     }
 
+    #[cfg(target_arch = "x86_64")]
+    pub fn nested(&self) -> bool {
+        self.config.nested
+    }
+
+    #[cfg(target_arch = "x86_64")]
+    pub fn kvm_hyperv(&self) -> bool {
+        self.config.kvm_hyperv
+    }
+
     /// Only create new vCPUs if there aren't any inactive ones to reuse
     fn create_vcpus(
         &mut self,