cleanup swiotlb initialization v4

[Christoph Hellwig]

Hi all,

this series tries to clean up the swiotlb initialization, including
that of swiotlb-xen.  To get there is also removes the x86 iommu table
infrastructure that massively obsfucates the initialization path.

Git tree:

    git://git.infradead.org/users/hch/misc.git swiotlb-init-cleanup

Gitweb:

    http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/swiotlb-init-cleanup

Changes since v3:
 - fix a compilation issue on some powerpc configfs
 - fix and cleanup how forced bounce buffering is enabled for
   guest memory encryption

Changes since v2:
 - make ppc_swiotlb_flags actually work again
 - also force enable swiotlb for guest encrypted memory to cater
   to hyperv which doesn't set the host encrypted memory flag

Changes since v1:
 - skip IOMMU initialization on Xen PV kernels
 - various small whitespace / typo fixes

Diffstat: