iommu/vt-d: Don't disable translation prior to OS handover

For all the copy-translation code to run, we have to keep
translation enabled in intel_iommu_init(). So remove the
code disabling it.

Tested-by: ZhenHua Li <zhen-hual@hp.com>
Tested-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>