powerpc/powernv: set power_save func after the idle states are initialized

pnv_init_idle_states() discovers supported idle states from the
device tree and does the required initialization. Set power_save
function pointer only after this initialization is done

Otherwise on machines which don't support nap, eg. Power9, the kernel
will crash when it tries to nap.
Reviewed-by: NGautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: NShreyas B. Prabhu <shreyas@linux.vnet.ibm.com>
Acked-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: NMichael Neuling <mikey@neuling.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/idle.c

@@ -285,6 +285,9 @@ static int __init pnv_init_idle_states(void)
 	}
 
 	pnv_alloc_idle_core_states();
+
+	if (supported_cpuidle_states & OPAL_PM_NAP_ENABLED)
+		ppc_md.power_save = power7_idle;
 out_free:
 	kfree(flags);
 out:

arch/powerpc/platforms/powernv/setup.c

@@ -315,7 +315,7 @@ define_machine(powernv) {
 	.get_proc_freq          = pnv_get_proc_freq,
 	.progress		= pnv_progress,
 	.machine_shutdown	= pnv_shutdown,
-	.power_save             = power7_idle,
+	.power_save             = NULL,
 	.calibrate_decr		= generic_calibrate_decr,
 #ifdef CONFIG_KEXEC
 	.kexec_cpu_down		= pnv_kexec_cpu_down,