powerpc/mm: Rework & cleanup page table freeing code path

That patch used to just add a hook to page table flushing but
pulling that string brought out a whole bunch of issues, so it
now does that and more:

 - We now make the RCU batching of page freeing SMP only, as I
believe it was intended initially. We make a few more things compile
to nothing on !CONFIG_SMP

 - Some macros are turned into functions, though that forced me to
out of line a few stuffs due to unsolvable include depenencies,
however it's probably better that way anyway, it's not -that-
critical code path.

 - 32-bit didn't call pte_free_finish() on tlb_flush() which means
that it wouldn't push out the batch to RCU for delayed freeing when
a bunch of page tables have been freed, they would just stay in there
until the batch gets full.

64-bit BookE will use that hook to maintain the virtually linear
page tables or the indirect entries in the TLB when using the
HW loader.

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

arch/powerpc/mm/tlb_hash64.c

@@ -154,6 +154,21 @@ void __flush_tlb_pending(struct ppc64_tlb_batch *batch)
 	batch->index = 0;
 }
 
+void tlb_flush(struct mmu_gather *tlb)
+{
+	struct ppc64_tlb_batch *tlbbatch = &__get_cpu_var(ppc64_tlb_batch);
+
+	/* If there's a TLB batch pending, then we must flush it because the
+	 * pages are going to be freed and we really don't want to have a CPU
+	 * access a freed page because it has a stale TLB
+	 */
+	if (tlbbatch->index)
+		__flush_tlb_pending(tlbbatch);
+
+	/* Push out batch of freed page tables */
+	pte_free_finish();
+}
+
 /**
  * __flush_hash_table_range - Flush all HPTEs for a given address range
  *                            from the hash table (and the TLB). But keeps