fs/Kconfig: make hugetlbfs a menuconfig

Hugetlb vmemmap default option (HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON)
is a sub-option to hugetlbfs, but it shows in the same level as hugetlbfs
itself, under "Pesudo filesystems".

Make the vmemmap option a sub-option to hugetlbfs, by changing hugetlbfs
into a menuconfig.  When moving it, fix a typo 'v' spot by Randy.

Link: https://lkml.kernel.org/r/20231124151902.1075697-1-peterx@redhat.com


Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>