x86/boot/tboot: Move tboot_force_iommu() to Intel IOMMU

tboot_force_iommu() is only called by the Intel IOMMU driver. Move the
helper into that driver. No functional change intended.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Steve Wahl <steve.wahl@hpe.com>
Link: https://lore.kernel.org/r/20220514014322.2927339-7-baolu.lu@linux.intel.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>