vdpa: Sync calls set/get config/status with cf_mutex

Add wrappers to get/set status and protect these operations with
cf_mutex to serialize these operations with respect to get/set config
operations.

Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20220105114646.577224-4-elic@nvidia.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>