memblock: reject non-page-aligned reserve_mem regions

When map->start or map->size is not page aligned,
reserved_mem_preserve() does not preserve the last one or two pages of
the region from map->start to map->start + map->size.

After kexec the new kernel reserves only the preserved pages, so those
pages are released to the buddy allocator. But
reserve_mem_find_by_name() still returns the whole region including
them, so they can be allocated while the subsystem is still using them.

So reject a reserve_mem= size or alignment that is not a multiple of
PAGE_SIZE to keep both map->start and map->size page aligned.

Fixes: 8375b76517cb ("kho: replace kho_preserve_phys() with kho_preserve_pages()")
Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Link: https://patch.msgid.link/20260905141526.1546478-1-ekffu200098@gmail.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>