mm/userfaultfd: disable userfaultfd-wp on x86_32

Userfaultfd-wp is not yet working on 32bit hosts, but it's accidentally
enabled previously.  Disable it.

Fixes: 5a281062af ("userfaultfd: wp: add WP pagetable tracking to x86")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hillf Danton <hdanton@sina.com>
Link: http://lkml.kernel.org/r/20200413141608.109211-1-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/Kconfig

@@ -149,7 +149,7 @@ config X86
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64
-	select HAVE_ARCH_USERFAULTFD_WP		if USERFAULTFD
+	select HAVE_ARCH_USERFAULTFD_WP         if X86_64 && USERFAULTFD
 	select HAVE_ARCH_VMAP_STACK		if X86_64
 	select HAVE_ARCH_WITHIN_STACK_FRAMES
 	select HAVE_ASM_MODVERSIONS