x86: remove duplicated extern force_iommu

Both iommu.h and dma-mapping.h have extern force_iommu. The latter
doesn't need to do.

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