libxl: colo: rearrange things in header files

libxl: colo: rearrange things in header files

We need to separate COLO code from common code as clean as possible.
With this patch, all COLO structures are now in libxl_colo.h.

It does the following:
1. Move two typedefs for libxl__domain_create_state{,cb} back to
   libxl_internal.h.
2. Move libxl__colo_save_state to libxl_colo.h.
3. Include libxl_internal.h in libxl_colo.h.
4. Move a bunch of colo typedefs to the top of libxl_internal.h.
5. Move the inclusion of libxl_colo.h to the right place in
   libxl_internal.h.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>