libxl: autogenerate _libxl_types.h

libxl: autogenerate _libxl_types.h

The libxl interface types are represented by a simple python data
structure (which could be parsed from a bespoke language in the
future).

This will allow the autogeneration of functions to free the component
members of the libxl types. In the future it may also enable auto
generation of type marshalling code for language bindings.

The generated file should be identical to before with the exception of
the "DO NOT EDIT" header.

It was unfortunately necessary to add explcit an dependency on
_libxl_types.h (indirectly via libxl.h) to all C files since the
autogenerated dependencies are not available in time.

[PATCH 04 of 16 of
 libxl: autogenerate type definitions and destructor functions]

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