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/init_32.c

@@ -54,8 +54,6 @@
 #endif
 #define MAX_LOW_MEM	CONFIG_LOWMEM_SIZE
 
-DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
-
 phys_addr_t total_memory;
 phys_addr_t total_lowmem;