add dma_get_ops to struct ia64_machine_vector

This adds dma_get_ops hook to struct ia64_machine_vector. We use
dma_get_ops() in arch/ia64/kernel/dma-mapping.c, which simply returns
the global dma_ops. This is for removing hwsw_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>