arch: x86_64: recommend Hyper-V paravirt TLB flush and cluster IPI

Adds three recommendation bits to CPUID 0x40000004.EAX so Windows / Hyper-V-
aware guests use the corresponding paravirtualized hypercalls instead of
falling back to architectural primitives. The hypercalls themselves are
emulated unconditionally by KVM and surfaced via the corresponding
KVM_CAP_HYPERV_* info caps; no userspace cap negotiation is needed because
KVM advertises support to the guest at hypercall-issue time:

  KVM_CAP_HYPERV_TLBFLUSH advertises HvFlush{VirtualAddressSpace,Ex,List,
                          ListEx} (per Documentation/virt/kvm/api.rst §8.18,
                          "Architectures: x86" — info-only cap).
  KVM_CAP_HYPERV_SEND_IPI advertises HvCallSendSyntheticClusterIpi{,Ex}
                          (api.rst §8.20, also info-only).

Leaf 0x40000004.EAX (HV_CPUID_ENLIGHTMENT_INFO):
  bit 1  LocalTlbFlushRecommended
  bit 2  RemoteTlbFlushRecommended
         These recommend HvFlushVirtualAddressSpace / HvFlushVirtualAddress
         List in place of architectural INVPCID / INVLPG broadcasts. Remote
         TLB shoot-down via hypercall lets the host skip vCPUs that are
         not currently scheduled, instead of waiting for them to receive
         and ack the IPI.
  bit 10 ClusterIpiRecommended
         Recommends HvCallSendSyntheticClusterIpi over per-target APIC ICR
         writes. A single hypercall can target up to 64 vCPUs (or all of
         them via the Ex variant) versus one VM exit per APIC access on
         the architectural path.

These bits depend on AccessVpIndex (0x40000003.EAX bit 6), which is now
advertised after the partition-privileges fix.

Sources:
  Microsoft Hypervisor Top-Level Functional Specification 7.4.5
  qemu/qemu docs/system/i386/hyperv.rst (hv-tlbflush, hv-ipi)
  Linux Documentation/virt/kvm/api.rst §8.18, §8.20

Author: CMGS

arch/src/x86_64/mod.rs

@@ -872,7 +872,10 @@ fn required_common_cpuid_updates(
         });
         cpuid.push(CpuIdEntry {
             function: 0x4000_0004,
-            eax: 1 << 5, // Recommend relaxed timing
+            eax: (1 << 1) // LocalTlbFlushRecommended
+                   | (1 << 2) // RemoteTlbFlushRecommended
+                   | (1 << 5) // RelaxedTimingRecommended
+                   | (1 << 10), // ClusterIpiRecommended (HvCallSendSyntheticClusterIpi)
             ..Default::default()
         });
         for i in 0x4000_0005..=0x4000_000a {