mm/mm_init: rename __init_reserved_page_zone to __init_page_from_nid

mm/mm_init: rename __init_reserved_page_zone to __init_page_from_nid

__init_reserved_page_zone() function finds the zone for pfn and nid and
performs initialization of a struct page with that zone and nid.  There is
nothing in that function about reserved pages and it is misnamed.

Rename it to __init_page_from_nid() to better reflect what the function
does.

Link: https://lkml.kernel.org/r/20250225083017.567649-2-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>