The vm-memory crate now supports Xen specific memory mappings via a
special feature: "xen".

Add a corresponding feature for vhost crate and add support for Xen
memory regions. Update various dependencies to align to the same version
of vm-memory crate.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Automatically enable the VhostUserProtocolFeatures::XEN_MMAP feature for
backends for Xen specific builds. With these the backends don't need to
enable this feature and can directly support Xen.

Suggested-by: Erik Schilling <erik.schilling@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Release a new version with Xen support.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Migrate to a newer version of the vhost and other dependencies and add
support for xen memory mappings. Add a corresponding xen feature for
vhost-user-backend crate.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Release a new version with Xen support.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>