memblock tests: Add simulation of physical memory

Allocation functions that return virtual addresses (with an exception
of _raw variant) clear the allocated memory after reserving it. This
requires valid memory ranges in memblock.memory.

Introduce memory_block variable to store memory that can be registered
with memblock data structure. Move assert.h and size.h includes to common.h
to share them between the test files.

Signed-off-by: Karolina Drobnik <karolinadrobnik@gmail.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Link: https://lore.kernel.org/r/dce115503c74a6936c44694b00014658a1bb6522.1646055639.git.karolinadrobnik@gmail.com