Revert "iommu/intel-iommu: Enable CONFIG_DMA_DIRECT_OPS=y and clean up intel_{alloc,free}_coherent()"

This commit may cause a less than required dma mask to be used for
some allocations, which apparently leads to module load failures for
iwlwifi sometimes.

This reverts commit d657c5c7.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Fabio Coatti <fabio.coatti@gmail.com>
Tested-by: Fabio Coatti <fabio.coatti@gmail.com>