x86/libxc: add an arch domain config parameter to xc_domain_create

x86/libxc: add an arch domain config parameter to xc_domain_create

With the addition of HVMlite the hypervisor now always requires a non-null
arch domain config, which is different between HVM and PV guests.

Add a new parameter to xc_domain_create that contains a pointer to an arch
domain config. If the pointer is null, create a default arch domain config
based on guest type.

Fix all the in-tree callers to provide a null arch domain config in order to
mimic previous behaviour.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>