arm64: KVM: Support X-Gene guest VCPU on APM X-Gene host
This patch allows us to have X-Gene guest VCPU when using KVM arm64
on APM X-Gene host.
We add KVM_ARM_TARGET_XGENE_POTENZA for X-Gene Potenza compatible
guest VCPU and we return KVM_ARM_TARGET_XGENE_POTENZA in kvm_target_cpu()
when running on X-Gene host with Potenza core.