memblock tests: add tests for memblock_*bottom_up functions

Add simple tests for memblock_set_bottom_up() and memblock_bottom_up().

Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Shaoqin Huang <shaoqin.huang@intel.com>
Signed-off-by: Rebecca Mckeever <remckee0@gmail.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Link: https://lore.kernel.org/r/b03701d2faeaf00f7184e4b72903de4e5e939437.1661578349.git.remckee0@gmail.com