sh: Move PMB debugfs entry initialization to later stage

... so the "sh_debugfs_root" is already available. Previously it
wasn't and in result its path was "/sys/kernel/debug/pmb" instead of
"/sys/kernel/debug/sh/pmb".
Signed-off-by: Pawel Moll <pawel.moll@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/mm/pmb.c

@@ -871,7 +871,7 @@ static int __init pmb_debugfs_init(void)
 
 	return 0;
 }
-postcore_initcall(pmb_debugfs_init);
+subsys_initcall(pmb_debugfs_init);
 
 #ifdef CONFIG_PM
 static int pmb_sysdev_suspend(struct sys_device *dev, pm_message_t state)