imx: mx31 use new formula for get_cpu_rev

Use new formula for get_cpu_rev, since we need to use this formula
to do runtime check for all i.MXes.

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Reviewed-by: Stefano Babic <sbabic@denx.de>
diff --git a/arch/arm/include/asm/arch-mx31/sys_proto.h b/arch/arm/include/asm/arch-mx31/sys_proto.h
index b0dfcba..1626442 100644
--- a/arch/arm/include/asm/arch-mx31/sys_proto.h
+++ b/arch/arm/include/asm/arch-mx31/sys_proto.h
@@ -8,6 +8,8 @@
 #ifndef _SYS_PROTO_H_
 #define _SYS_PROTO_H_
 
+#include "../arch-imx/cpu.h"
+
 struct mxc_weimcs {
 	u32 upper;
 	u32 lower;