Install runtime headers for mirage-xen.

- Provides C code with headers that match the minimal libc
  and OCaml functions they will be linked against.
Use the mini-os APIs for mapping in grants rather than our internal fns

Our 'map_onto' hack doesn't seem to work on ARM mini-os, so let's use the
official mini-os functions instead.

Signed-off-by: David Scott <dave.scott@citrix.com>
stub_gnttab_mapv_batched should call gntmap_map_grant_refs

Now that we've switched to an 'allocating' interface, we have to
implement both individual mapping and batch mapping.

Signed-off-by: David Scott <dave.scott@citrix.com>
xen: use the 'allocating' style of 'gntshr' (aka gntmap)

The new mini-os APIs are allocating in the sense that they return
fresh buffers containing foreign grant-mapped pages rather than
requiring us to pass in our own buffers.

One day everything will be this style and we can get rid of the
dead code.

Signed-off-by: David Scott <dave.scott@citrix.com>
Merge branch 'minios-gntmap' of git://github.com/djs55/mirage-platform
Sync CHANGES