xen/domain: Introduce a new sanitise_domain_config() helper

xen/domain: Introduce a new sanitise_domain_config() helper

Call it from the head of domain_create() (before doing any memory
allocations), which will apply the checks to dom0 as well as domU's.

For now, just subsume the XEN_DOMCTL_CDF_* check from XEN_DOMCTL_createdomain.

In an effort to aid future developoment, leave a debug printk() identifying
the cause of sanitisation failures.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>