tools: ocaml: autogenerate xl datatype definitions and ocaml<->C conversion

tools: ocaml: autogenerate xl datatype definitions and ocaml<->C conversion

The method by which ocaml converts between ocaml types and C
datastructures is based around explicit matching of field indexes
within the ocaml data type to C structure members which is error prone
to write and fragile to maintain (as evidenced by the difference
between the existing hand coded support and the autogenerated code
which shows how out of date the ocaml bindings have
become). Autogenerating these types should reduce these problems.

There is a short list of types which are blacklisted and not
autogenerated because I expect them to change significantly in the
future due to changes to the IDL type (fixing up the TaggedUnion
class) so I didn't want to spend the time to implement the necessary
autogenerator features just yet..

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson.citrix.com>
Committed-by: Ian Jackson <ian.jackson.citrix.com>