tools/include: Add debugfs.h stub

Add a dummy debugfs.h header.

Signed-off-by: Karolina Drobnik <karolinadrobnik@gmail.com>
Signed-off-by: Mike Rapoport <rppt@kernel.org>
Link: https://lore.kernel.org/r/80fceff27934094873cc3f0656d22e802dfcce78.1643796665.git.karolinadrobnik@gmail.com