xen: Add some dummy headers for PVH mode

xen: Add some dummy headers for PVH mode

With Xen PVH mode adding a new machine type the machine related headers
need to be present for the build to succeed. Most of the headers just
need to include the related common i386 headers. Add those to the tree.

Note that xen_pvh/int.h needs to include pc/int_types.h instead of
pc/int.h in order to avoid the definition of grub_bios_interrupt().

xen_pvh/memory.h needs to include coreboot/memory.h (like some other
<machine>/memory.h do as well) as this contains just the needed stubs.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-by: Hans van Kranenburg <hans@knorrie.org>