x86, ia64: remove duplicated swiotlb code

This adds swiotlb_map_page and swiotlb_unmap_page to lib/swiotlb.c and
remove IA64 and X86's swiotlb_map_page and swiotlb_unmap_page.

This also removes unnecessary swiotlb_map_single, swiotlb_map_single_attrs,
swiotlb_unmap_single and swiotlb_unmap_single_attrs.

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>