mm/Kconfig: make userfaultfd a menuconfig

PTE_MARKER_UFFD_WP is a subconfig for userfaultfd.  To make it clear,
switch to use menuconfig for userfaultfd.

Link: https://lkml.kernel.org/r/20231123224204.1060152-1-peterx@redhat.comSigned-off-by: Peter Xu <peterx@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/Kconfig

@@ -1201,13 +1201,6 @@ config ANON_VMA_NAME
 	  area from being merged with adjacent virtual memory areas due to the
 	  difference in their name.
 
-config USERFAULTFD
-	bool "Enable userfaultfd() system call"
-	depends on MMU
-	help
-	  Enable the userfaultfd() system call that allows to intercept and
-	  handle page faults in userland.
-
 config HAVE_ARCH_USERFAULTFD_WP
 	bool
 	help
@@ -1218,6 +1211,14 @@ config HAVE_ARCH_USERFAULTFD_MINOR
 	help
 	  Arch has userfaultfd minor fault support
 
+menuconfig USERFAULTFD
+	bool "Enable userfaultfd() system call"
+	depends on MMU
+	help
+	  Enable the userfaultfd() system call that allows to intercept and
+	  handle page faults in userland.
+
+if USERFAULTFD
 config PTE_MARKER_UFFD_WP
 	bool "Userfaultfd write protection support for shmem/hugetlbfs"
 	default y
@@ -1227,6 +1228,7 @@ config PTE_MARKER_UFFD_WP
 	  Allows to create marker PTEs for userfaultfd write protection
 	  purposes.  It is required to enable userfaultfd write protection on
 	  file-backed memory types like shmem and hugetlbfs.
+endif # USERFAULTFD
 
 # multi-gen LRU {
 config LRU_GEN