x86/HVM: prevent use-after-free when destroying a domain

x86/HVM: prevent use-after-free when destroying a domain

hvm_domain_relinquish_resources() can free certain domain resources
which can still be accessed, e.g. by HVMOP_set_param, while the domain
is being cleaned up.

This is CVE-2015-0361 / XSA-116.

Signed-off-by: Mihai Donțu <mdontu@bitdefender.com>
Tested-by: Răzvan Cojocaru <rcojocaru@bitdefender.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>