Add <linux/errno.h> as a wrapper of <asm-generic/errno.h>

This will be used to consolidate errno.h variants.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>

include/linux/errno.h

+#ifndef _LINUX_ERRNO_H
+#define _LINUX_ERRNO_H
+
+#include <asm-generic/errno.h>
+
+#endif