dm_op: convert HVMOP_*ioreq_server*

dm_op: convert HVMOP_*ioreq_server*

The definitions of HVM_IOREQSRV_BUFIOREQ_* have to persist as they are
already in use by callers of the libxc interface.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>