s390/mm: use generic mm_hooks

s390/mm: use generic mm_hooks

CVE-2017-5754

With git commit 3446c13b268af86391d06611327006b059b8bab1
"s390/mm: four page table levels vs. fork"
s390 dropped its architecture specific version of arch_dup_mmap.

Now all functions defined by include/asm-generic/mm_hooks.h are
identical to the s390 versions. Use the generic header.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
(cherry picked from commit 8e58ab5c6563e3cc94029853471a36b87b4716eb)
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>