mm: hugetlb: log time needed to allocate hugepages

Having this information allows users to easily tune the
hugepages_node_threads parameter.

Link: https://lkml.kernel.org/r/20250227-hugepage-parameter-v2-3-7db8c6dc0453@cyberus-technology.de


Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>