set up dma_ops appropriately

This patch introduces a global pointer, dma_ops, which points to an
appropriate dma_mapping_ops that the kernel should use. This is a
common way to handle multiple dma_mapping_ops (X86, POWER, and SPARC).

dma_ops is set in platform_dma_init. We also set it by hand where
machvec_init is callev via subsys_initcall.

- IA64_DIG_VTD uses vtd_dma_ops.
- IA64_HP_ZX1 uses sba_dma_ops.
- IA64_HP_ZX1_SWIOTLB uses hwsw_dma_ops.
- IA64_SGI_SN2 uses sn_dma_ops.
- The rest use swiotlb_dma_ops.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/ia64/hp/common/hwsw_iommu.c

@@ -56,9 +56,12 @@ use_swiotlb (struct device *dev)
 	return dev && dev->dma_mask && !hwiommu_dma_supported(dev, *dev->dma_mask);
 }
 
+struct dma_mapping_ops hwsw_dma_ops;
+
 void __init
 hwsw_init (void)
 {
+	dma_ops = &hwsw_dma_ops;
 	/* default to a smallish 2MB sw I/O TLB */
 	if (swiotlb_late_init_with_default_size (2 * (1<<20)) != 0) {
 #ifdef CONFIG_IA64_GENERIC