Revert "[POWERPC] DMA 4GB boundary protection"

This reverts commit 618d3adc351a24c4c48437c767befb88ca2d199d, because
it is superseded by 569975591c5530fdc9c7a3c45122e5e46f075a74.

arch/powerpc/kernel/iommu.c

@@ -89,7 +89,6 @@ static unsigned long iommu_range_alloc(struct iommu_table *tbl,
                                        unsigned int align_order)
 { 
 	unsigned long n, end, i, start;
-	unsigned long start_addr, end_addr;
 	unsigned long limit;
 	int largealloc = npages > 15;
 	int pass = 0;
@@ -160,15 +159,6 @@ static unsigned long iommu_range_alloc(struct iommu_table *tbl,
 		}
 	}
 
-	/* DMA cannot cross 4 GB boundary */
-	start_addr = (n + tbl->it_offset) << PAGE_SHIFT;
-	end_addr = (end + tbl->it_offset) << PAGE_SHIFT;
-	if ((start_addr >> 32) != (end_addr >> 32)) {
-		end_addr &= 0xffffffff00000000l;
-		start = (end_addr >> PAGE_SHIFT) - tbl->it_offset;
-		goto again;
-	}
-
 	for (i = n; i < end; i++)
 		if (test_bit(i, tbl->it_map)) {
 			start = i+1;