target/smp: use a struct list_head to hold the smp targets

Instead of reinventing a simply linked list, reuse the list helper
for the list of targets in a smp cluster.
Using the existing helper, that implements a double linked list,
makes trivial going through the list in reverse order.

Change-Id: Ib36ad2955f15cd2a601b0b9e36ca6d948b12d00f
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6783
Tested-by: jenkins

src/target/smp.h

@@ -19,10 +19,11 @@
 #ifndef OPENOCD_TARGET_SMP_H
 #define OPENOCD_TARGET_SMP_H
 
+#include <helper/list.h>
 #include "server/server.h"
 
 #define foreach_smp_target(pos, head) \
-	for (pos = head; (pos); pos = pos->next)
+	list_for_each_entry(pos, head, lh)
 
 extern const struct command_registration smp_command_handlers[];