memblock tests: Add skeleton of the memblock simulator

Add basic project files, together with local stubs of required headers.
Update tools/include/slab.h to include definitions used by memblock.

Signed-off-by: Karolina Drobnik <karolinadrobnik@gmail.com>
Signed-off-by: Mike Rapoport <rppt@kernel.org>
Link: https://lore.kernel.org/r/d296fceb023a04b316a31fbff9acf1e76ac684e4.1643796665.git.karolinadrobnik@gmail.com