xen/arch/*: add struct domain parameter to arch_do_domctl

xen/arch/*: add struct domain parameter to arch_do_domctl

Since the arch-independent do_domctl function now RCU locks the domain
specified by op->domain, pass the struct domain to the arch-specific
domctl function and remove the duplicate per-subfunction locking.

This also removes two get_domain/put_domain call pairs (in
XEN_DOMCTL_assign_device and XEN_DOMCTL_deassign_device), replacing
them with RCU locking.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Acked-by: Tim Deegan <tim@xen.org>
Acked-by: Jan Beulich <jbeulich@suse.com>
Committed-by: Keir Fraser <keir@xen.org>