iommu: Restore iommu_flush_iotlb_all()

This patch restores the iommu_flush_iotlb_all() function.
Commit

	69e5a175 ("iommu: Remove useless flush from iommu_create_device_direct_mappings()")

claims it removed the last call-site, except it did not. There is still
at least one caller in

	drivers/gpu/drm/msm/msm_iommu.c

so keep the function around until all call-sites are updated.

Cc: Jason Gunthorpe <jgg@ziepe.ca>
Fixes: 69e5a175 ("iommu: Remove useless flush from iommu_create_device_direct_mappings()")
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>