KVM: x86: Introduce __kvm_get_hypervisor_cpuid() helper

Similar to kvm_find_kvm_cpuid_features()/__kvm_find_kvm_cpuid_features(),
introduce a helper to search for the specific hypervisor signature in any
struct kvm_cpuid_entry2 array, not only in vcpu->arch.cpuid_entries.

No functional change intended.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20240228101837.93642-2-vkuznets@redhat.com
Signed-off-by: Sean Christopherson <seanjc@google.com>