[MIPS] Introduce _machine_restart

Handles machine specific functions by using weak functions.

Signed-off-by: Shinya Kuribayashi <skuribay@ruby.dti.ne.jp>
diff --git a/board/purple/purple.c b/board/purple/purple.c
index 74718af..13a1455 100644
--- a/board/purple/purple.c
+++ b/board/purple/purple.c
@@ -29,6 +29,7 @@
 #include <asm/io.h>
 #include <asm/addrspace.h>
 #include <asm/cacheops.h>
+#include <asm/reboot.h>
 
 #include "sconsole.h"
 
@@ -52,6 +53,13 @@
 extern int	asc_serial_tstc 	(void);
 extern void	asc_serial_setbrg 	(void);
 
+void _machine_restart(void)
+{
+	void (*f)(void) = (void *) 0xbfc00000;
+
+	f();
+}
+
 static void sdram_timing_init (ulong size)
 {
 	register uint pass;