Cédric pointed out that XIVE IPI information exported via sysfs
(debug/powerpc/xive) display empty lines for processors which are
not online.

Switch to using for_each_online_cpu() so that information is
displayed for online-only processors.

Reported-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Sachin Sant <sachinp@linux.ibm.com>
--- 
diff -Naurp a/arch/p werpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
--- a/arch/powerpc/sysdev/xive/common.c	2022-01-05 08:52:59.460118219 -0500
+++ b/arch/powerpc/sysdev/xive/common.c	2022-01-06 02:34:20.994513145 -0500
@@ -1791,7 +1791,7 @@ static int xive_ipi_debug_show(struct se
 	if (xive_ops->debug_show)
 		xive_ops->debug_show(m, private);
 
-	for_each_possible_cpu(cpu)
+	for_each_online_cpu(cpu)
 		xive_debug_show_ipi(m, cpu);
 	return 0;
 }