x86: Calgary: Convert detect_calgary() to use iommu_init hook

This changes detect_calgary() to set init_calgary() to
iommu_init hook if detect_calgary() finds the Calgary IOMMU.

We can kill the code to check if we found the IOMMU in
init_calgary() since detect_calgary() sets init_calgary() only
when it found the IOMMU.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Muli Ben-Yehuda <muli@il.ibm.com>
Cc: chrisw@sous-sol.org
Cc: dwmw2@infradead.org
Cc: joerg.roedel@amd.com
LKML-Reference: <1257849980-22640-3-git-send-email-fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>