swiotlb: replace architecture-specific swiotlb.h with linux/swiotlb.h

Impact: cleanup

This replaces architecture-specific swiotlb.h (X86 and IA64) with
linux/swiotlb.h.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>