tools/include: Add mm.h file

Add a stubbed mm.h file with dummy page-related definitions,
memory alignment and physical to virtual address conversions,
so they can be used in testing.

Signed-off-by: Karolina Drobnik <karolinadrobnik@gmail.com>
Signed-off-by: Mike Rapoport <rppt@kernel.org>
Link: https://lore.kernel.org/r/e8b83d96fec95f3556e80f001d9d5cbe18b8ad5f.1643796665.git.karolinadrobnik@gmail.com