Add basic errno support.

Needed for hash table support; probably useful in a lot of other
places as well.

Signed-off-by: Wolfgang Denk <wd@denx.de>

include/errno.h

@@ -0,0 +1,9 @@
+#ifndef _ERRNO_H
+
+#include <asm-generic/errno.h>
+
+extern int errno;
+
+#define __set_errno(val) do { errno = val; } while (0)
+
+#endif /* _ERRNO_H */