AMD/IOMMU: Move headers to be local

AMD/IOMMU: Move headers to be local

We currently have amd-iommu-defs.h, amd-iommu-proto.h and amd-iommu.h, and no
references outside of the AMD IOMMU driver.

Keep iommu-defs.h as is, but merge amd-iommu.h and amd-iommu-proto.h to just
iommu.h, and move them both into drivers/passthrough/amd/.  (While merging,
drop the bogus #pragma pack around the *_entry structures.)

Take the opportunity to trim the include lists, including x86/mm/p2m.c
which (AFAICT) hasn't needed this include since c/s aef3f2275 "x86/mm/p2m:
break into common, pt-implementation and pod parts" in 2011.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>