powerpc/mm: Move around mmu_gathers definition on 64-bit

The definition for the global structure mmu_gathers, used by generic code,
is currently defined in multiple places not including anything used by
64-bit Book3E. This changes it by moving to one place common to all
processors.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/mm/tlb_hash64.c

@@ -33,11 +33,6 @@
 
 DEFINE_PER_CPU(struct ppc64_tlb_batch, ppc64_tlb_batch);
 
-/* This is declared as we are using the more or less generic
- * arch/powerpc/include/asm/tlb.h file -- tgall
- */
-DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
-
 /*
  * A linux PTE was changed and the corresponding hash table entry
  * neesd to be flushed. This function will either perform the flush