xen idle: make xen-specific macro xen-specific

This macro is only invoked by Xen,
so make its definition specific to Xen.

> set_pm_idle_to_default()
< xen_set_default_idle()

Signed-off-by: Len Brown <len.brown@intel.com>
Cc: xen-devel@lists.xensource.com

arch/x86/xen/setup.c

@@ -561,7 +561,7 @@ void __init xen_arch_setup(void)
 #endif
 	disable_cpuidle();
 	disable_cpufreq();
-	WARN_ON(set_pm_idle_to_default());
+	WARN_ON(xen_set_default_idle());
 	fiddle_vdso();
 #ifdef CONFIG_NUMA
 	numa_off = 1;