tools/libxc: Fix domid parameter types

tools/libxc: Fix domid parameter types

Mixed throughout libxc are uint32_t, int, and domid_t for domid parameters.
With a signed type, and an explicitly 16-bit type, it is exceedingly difficult
to construct an INVALID_DOMID constant which works with all of them.  (The
main problem being that domid_t gets unconditionally zero extended when
promoted to int for arithmatic.)

Libxl uses uint32_t consistently everywhere, so alter libxc to match.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Release-acked-by: Julien Grall <julien.grall@linaro.org>
[ wei: fix compilation error in libxl ]
Signed-off-by: Wei Liu <wei.liu2@citrix.com>