[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/incaip/incaip.c b/board/incaip/incaip.c
index dbf0ecc..c624b3d 100644
--- a/board/incaip/incaip.c
+++ b/board/incaip/incaip.c
@@ -26,9 +26,15 @@
 #include <asm/addrspace.h>
 #include <asm/inca-ip.h>
 #include <asm/io.h>
+#include <asm/reboot.h>
 
 extern uint incaip_get_cpuclk(void);
 
+void _machine_restart(void)
+{
+	*INCA_IP_WDT_RST_REQ = 0x3f;
+}
+
 static ulong max_sdram_size(void)
 {
 	/* The only supported SDRAM data width is 16bit.