KVM: x86: Move guts of kvm_arch_vcpu_setup() into kvm_arch_vcpu_create()

Fold setup() into create() now that the two are called back-to-back by
common KVM code.  This paves the way for removing kvm_arch_vcpu_setup().

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>