powerpc/xmon: Dump XIVE information for online-only processors.

dxa command in XMON debugger iterates through all possible processors.
As a result, empty lines are printed even for processors which are not
online.

CPU 47:pp=00 CPPR=ff IPI=0x0040002f PQ=-- EQ idx=699 T=0 00000000 00000000
CPU 48:
CPU 49:

Restrict XIVE information(dxa) to be displayed for online processors only.

Signed-off-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/164139226833.12930.272224382183014664.sendpatchset@MacBook-Pro.local

Author: sacsant

arch/powerpc/xmon/xmon.c

@@ -2817,12 +2817,12 @@ static void dump_all_xives(void)
 {
 	int cpu;
 
-	if (num_possible_cpus() == 0) {
+	if (num_online_cpus() == 0) {
 		printf("No possible cpus, use 'dx #' to dump individual cpus\n");
 		return;
 	}
 
-	for_each_possible_cpu(cpu)
+	for_each_online_cpu(cpu)
 		dump_one_xive(cpu);
 }