This also removes the need to use vmlist_lock
on PV by tracking the allocated xenbus rings.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
[v1: Fix compile error when XENBUS_FRONTEND is defined as module]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
¡âíY•Vx