memblock tests: add new pageblock related macro

Add new pageblock_start_pfn() and pageblock_align() macro which are needed
by memblock tests.

Link: https://lkml.kernel.org/r/20220907082643.186979-1-wangkefeng.wang@huawei.com


Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>