Add common orderly_poweroff()

Various pieces of code around the kernel want to be able to trigger an
orderly poweroff.  This pulls them together into a single
implementation.

By default the poweroff command is /sbin/poweroff, but it can be set
via sysctl: kernel/poweroff_cmd.  This is split at whitespace, so it
can include command-line arguments.

This patch replaces four other instances of invoking either "poweroff"
or "shutdown -h now": two sbus drivers, and acpi thermal
management.

sparc64 has its own "powerd"; still need to determine whether it should
be replaced by orderly_poweroff().

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Acked-by: Len Brown <lenb@kernel.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Andi Kleen <ak@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David S. Miller <davem@davemloft.net>
diff --git a/drivers/sbus/char/envctrl.c b/drivers/sbus/char/envctrl.c
index 8328aca..dadabef1 100644
--- a/drivers/sbus/char/envctrl.c
+++ b/drivers/sbus/char/envctrl.c
@@ -26,6 +26,7 @@
 #include <linux/ioport.h>
 #include <linux/miscdevice.h>
 #include <linux/kmod.h>
+#include <linux/reboot.h>
 
 #include <asm/ebus.h>
 #include <asm/uaccess.h>
@@ -966,10 +967,6 @@
 static void envctrl_do_shutdown(void)
 {
 	static int inprog = 0;
-	static char *envp[] = {	
-		"HOME=/", "TERM=linux", "PATH=/sbin:/usr/sbin:/bin:/usr/bin", NULL };
-	char *argv[] = { 
-		"/sbin/shutdown", "-h", "now", NULL };	
 	int ret;
 
 	if (inprog != 0)
@@ -977,7 +974,7 @@
 
 	inprog = 1;
 	printk(KERN_CRIT "kenvctrld: WARNING: Shutting down the system now.\n");
-	ret = call_usermodehelper("/sbin/shutdown", argv, envp, 0);
+	ret = orderly_poweroff(true);
 	if (ret < 0) {
 		printk(KERN_CRIT "kenvctrld: WARNING: system shutdown failed!\n"); 
 		inprog = 0;  /* unlikely to succeed, but we could try again */