include/types.h: Add generic enum for error codes

The idea is that instead of:
 if (do_something()) do_something_else();
It is more readable to write:
 if (do_something() != CB_SUCCESS) handle_error();

Change-Id: I4fa5a6f2d2960cd747fda6602bdfff6aef08f8e2
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/4264
Tested-by: build bot (Jenkins)
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/include/types.h

@@ -21,5 +21,19 @@
 #define __TYPES_H
 #include <stdint.h>
 #include <stddef.h>
-#endif
 
+/**
+ * Coreboot error codes
+ *
+ * When building functions that return a status or an error code, use cb_err as
+ * the return type. When failure reason needs to be communicated by the return
+ * value, define a it here. Start new enum groups with values in decrements of
+ * 100.
+ */
+enum cb_err {
+	CB_SUCCESS = 0,		/**< Call completed succesfully */
+	CB_ERR = -1,		/**< Generic error code */
+	CB_ERR_ARG = -2,	/**< Invalid argument */
+};
+
+#endif /* __TYPES_H */