Extend the existing dummy mapcache_lock/unlock macros to cover all of
xen-mapcache.c.  This prepares for unlocked memory access, when parts
of exec.c will not be protected by the BQL.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>