memblock tests: Add memblock_add_node test

Add a simple test for NUMA-aware variant of memblock_add function.

Signed-off-by: Karolina Drobnik <karolinadrobnik@gmail.com>
Signed-off-by: Mike Rapoport <rppt@kernel.org>
Link: https://lore.kernel.org/r/e2d0e6dd264c8c169242b556f7c5b12153f3dee5.1643796665.git.karolinadrobnik@gmail.com