powerpc: fix build of epapr_paravirt on 64-bit book3s

This fixes an allyesconfig build break introduced by commit
7762b1ed7aaee223230793fcee80672e2e3aa7a8 "powerpc: move epapr paravirt
init of power_save to an initcall".
Signed-off-by: Scott Wood <scottwood@freescale.com>
Cc: Stuart Yoder <stuart.yoder@freescale.com>

arch/powerpc/kernel/epapr_paravirt.c

@@ -73,8 +73,10 @@ int __init epapr_paravirt_early_init(void)
 
 static int __init epapr_idle_init(void)
 {
+#if !defined(CONFIG_64BIT) || defined(CONFIG_PPC_BOOK3E_64)
 	if (epapr_has_idle)
 		ppc_md.power_save = epapr_ev_idle;
+#endif
 
 	return 0;
 }