arch/tile: enable ZONE_DMA for tilegx

This is required for PCI root complex legacy support and USB OHCI root
complex support.  With this change tilegx now supports allocating memory
whose PA fits in 32 bits.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
diff --git a/arch/tile/mm/init.c b/arch/tile/mm/init.c
index a2417a0..ef29d6c 100644
--- a/arch/tile/mm/init.c
+++ b/arch/tile/mm/init.c
@@ -733,16 +733,15 @@
 	for_each_zone(z) {
 		unsigned long start, end;
 		int nid = z->zone_pgdat->node_id;
+#ifdef CONFIG_HIGHMEM
 		int idx = zone_idx(z);
+#endif
 
 		start = z->zone_start_pfn;
-		if (start == 0)
-			continue;  /* bootmem */
 		end = start + z->spanned_pages;
-		if (idx == ZONE_NORMAL) {
-			BUG_ON(start != node_start_pfn[nid]);
-			start = node_free_pfn[nid];
-		}
+		start = max(start, node_free_pfn[nid]);
+		start = max(start, max_low_pfn);
+
 #ifdef CONFIG_HIGHMEM
 		if (idx == ZONE_HIGHMEM)
 			totalhigh_pages += z->spanned_pages;