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/kernel/pci-swiotlb.c

@@ -37,6 +37,12 @@ struct dma_mapping_ops swiotlb_dma_ops = {
 	.mapping_error = swiotlb_dma_mapping_error,
 };
 
+void swiotlb_dma_init(void)
+{
+	dma_ops = &swiotlb_dma_ops;
+	swiotlb_init();
+}
+
 void __init pci_swiotlb_init(void)
 {
 	if (!iommu_detected) {