Add tests for memblock_alloc_node()

Add tests for memblock_alloc_node()

This test is aimed at verifying the memblock_alloc_node() to work as
expected, so setting the correct NUMA node for the new allocated
region. The memblock_alloc_node() is called directly without using any
stub. The core check is between the requested NUMA node and the `nid`
field inside the memblock_region structure. These two are supposed to
be equal for the test to succeed.

Signed-off-by: Claudio Migliorelli <claudio.migliorelli@mail.polimi.it>
Link: https://lore.kernel.org/r/ea5e938e-6b74-b188-af59-4b94b18bc0@mail.polimi.it
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>