s390/kdump: Disable mmap for s390

The kdump mmap patch series (git commit 83086978c6) directly
map the PT_LOADs to memory. On s390 this does not work because the
copy_from_oldmem() function swaps [0,crashkernel size] with
[crashkernel base, crashkernel base+crashkernel size]. The swap
int copy_from_oldmem() was done in order correctly implement /dev/oldmem.

See: http://marc.info/?l=kexec&m=136940802511603&w=2

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

fs/proc/vmcore.c

@@ -223,7 +223,7 @@ static inline char *alloc_elfnotes_buf(size_t notes_sz)
  * regions in the 1st kernel pointed to by PT_LOAD entries) into
  * virtually contiguous user-space in ELF layout.
  */
-#ifdef CONFIG_MMU
+#if defined(CONFIG_MMU) && !defined(CONFIG_S390)
 static int mmap_vmcore(struct file *file, struct vm_area_struct *vma)
 {
 	size_t size = vma->vm_end - vma->vm_start;