add socket wrapper for at framework

you can use at framework to send/recv data in socket API
example: see examples\tcp_through_module_based_at_socket
project: see board\TencentOS_tiny_EVB_MX_Plus\KEIL\tcp_through_module_based_at_socket

arch/msp430/common/include/tos_cpu_def.h

@@ -9,5 +9,8 @@
 #define CPU_STK_GROWTH_ASCENDING    1
 #define CPU_STK_GROWTH_DESCENDING   2
 
+#define CPU_BYTE_ORDER_LITTLE_ENDIAN    1
+#define CPU_BYTE_ORDER_BIG_ENDIAN       2
+
 #endif /* _TOS_CPU_DEF_H_ */