memblock tests: Add memblock_free tests

Add checks for removing a region from reserved memory in different
scenarios:
 - The requested region matches one in the collection of reserved
   memory regions
 - The requested region does not exist in memblock.reserved
 - The region overlaps with one of the entries: from the top (its
   end address is bigger than the base of the existing region) or
   from the bottom (its base address is smaller than the end address
   of one of the regions)
 - The region is within an already defined region

Signed-off-by: Karolina Drobnik <karolinadrobnik@gmail.com>
Signed-off-by: Mike Rapoport <rppt@kernel.org>
Link: https://lore.kernel.org/r/30af95c82754ad8029404c3b528a5ef1c05d1ed6.1643796665.git.karolinadrobnik@gmail.com