include: Add __packed define for packed structures

This patch adds __packed define for specifying packed
attribute of structures.

Signed-off-by: Anup Patel <anup.patel@wdc.com>

include/sbi/sbi_types.h

@@ -54,6 +54,7 @@ typedef unsigned long		physical_size_t;
 
 #define NULL			((void *)0)
 
+#define __packed		__attribute__((packed))
 #define __noreturn		__attribute__((noreturn))
 
 #endif