ARM: xen: only set pm function ptrs for Xen guests

xen_pm_init was unconditionally setting pm_power_off and arm_pm_restart
function pointers. This breaks multi-platform kernels. Make this
conditional on running as a Xen guest and make it a late_initcall to
ensure it is setup after platform code for Dom0.
Signed-off-by: NRob Herring <rob.herring@calxeda.com>
Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
CC: stable@vger.kernel.org

arch/arm/xen/enlighten.c

@@ -272,12 +272,15 @@ core_initcall(xen_guest_init);
 
 static int __init xen_pm_init(void)
 {
+	if (!xen_domain())
+		return -ENODEV;
+
 	pm_power_off = xen_power_off;
 	arm_pm_restart = xen_restart;
 
 	return 0;
 }
-subsys_initcall(xen_pm_init);
+late_initcall(xen_pm_init);
 
 static irqreturn_t xen_arm_callback(int irq, void *arg)
 {