tools/include: Add io.h stub

Add a dummy io.h header.

Signed-off-by: Karolina Drobnik <karolinadrobnik@gmail.com>
Signed-off-by: Mike Rapoport <rppt@kernel.org>
Link: https://lore.kernel.org/r/3e8d42cbd01382d956d393cf3bb2a6d639dfdd97.1643796665.git.karolinadrobnik@gmail.com