powerpc/8xx: add system_reset_exception

When the watchdog is in NMI mode, the system reset interrupt is
generated when the watchdog counter expires.
Signed-off-by: NChristophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: NScott Wood <oss@buserror.net>

arch/powerpc/kernel/head_8xx.S

@@ -226,7 +226,7 @@ i##n:								\
 			  ret_from_except)
 
 /* System reset */
-	EXCEPTION(0x100, Reset, unknown_exception, EXC_XFER_STD)
+	EXCEPTION(0x100, Reset, system_reset_exception, EXC_XFER_STD)
 
 /* Machine check */
 	. = 0x200

arch/powerpc/kernel/traps.c

@@ -273,7 +273,6 @@ void _exception(int signr, struct pt_regs *regs, int code, unsigned long addr)
 	force_sig_info(signr, &info, current);
 }
 
-#ifdef CONFIG_PPC64
 void system_reset_exception(struct pt_regs *regs)
 {
 	/* See if any machine dependent calls */
@@ -291,6 +290,7 @@ void system_reset_exception(struct pt_regs *regs)
 	/* What should we do here? We could issue a shutdown or hard reset. */
 }
 
+#ifdef CONFIG_PPC64
 /*
  * This function is called in real mode. Strictly no printk's please.
  *