[swsusp] Restore software_suspend() call.

- Allows 'backdoor' interface to swsusp, as requested by Pavel. 

- Simply a wrapper to pm_suspend(), though guaranteeing that swsusp is used,
  and system is shutdown (and put into low-power state).

- Call in sys_reboot() changed back to call to software_suspend().

include/linux/suspend.h

@@ -53,6 +53,7 @@ extern suspend_pagedir_t *pagedir_nosave __nosavedata;
 extern void do_suspend_lowlevel(int resume);
 extern void do_suspend_lowlevel_s4bios(int resume);
 
+extern int software_suspend(void);
 #else	/* CONFIG_SOFTWARE_SUSPEND */
 static inline int software_suspend(void)
 {

kernel/power/swsusp.c

@@ -948,6 +948,17 @@ int swsusp_free(void)
 	return 0;
 }
 
+
+int software_suspend(void)
+{
+	struct pm_ops swsusp_ops = {
+		.pm_disk_mode	= PM_DISK_SHUTDOWN,
+	};
+
+	pm_set_ops(&swsusp_ops);
+	return pm_suspend(PM_SUSPEND_DISK);
+}
+
 static int __init resume_setup(char *str)
 {
 	if (strlen(str))

kernel/sys.c

@@ -456,7 +456,7 @@ asmlinkage long sys_reboot(int magic1, int magic2, unsigned int cmd, void __user
 
 #ifdef CONFIG_SOFTWARE_SUSPEND
 	case LINUX_REBOOT_CMD_SW_SUSPEND:
-		if (!pm_suspend(PM_SUSPEND_DISK))
+		if (!software_suspend())
 			break;
 		do_exit(0);
 		break;