xen: additionally restrict xenforeignmemory operations

Commit f0f272baf3a7 "xen: use libxendevice model to restrict operations"
added a command-line option (-xen-domid-restrict) to limit operations
using the libxendevicemodel API to a specified domid. The commit also
noted that the restriction would be extended to cover operations issued
via other xen libraries by subsequent patches.

My recent Xen patch [1] added a call to the xenforeignmemory API to allow
it to be restricted. This patch now makes use of that new call when the
-xen-domid-restrict option is passed.

[1] http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=5823d6eb

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
