x86: Add iommu_init to x86_init_ops

We call the detections functions of all the IOMMUs then all
their initialization functions. The latter is pointless since we
don't detect multiple different IOMMUs. What we need to do is
calling the initialization function of the detected IOMMU.

This adds iommu_init hook to x86_init_ops so if an IOMMU
detection function can set its initialization function to the
hook.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: chrisw@sous-sol.org
Cc: dwmw2@infradead.org
Cc: joerg.roedel@amd.com
Cc: muli@il.ibm.com
LKML-Reference: <1257849980-22640-2-git-send-email-fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>