pds_vdpa: subscribe to the pds_core events

Register for the pds_core's notification events, primarily to
find out when the FW has been reset so we can pass this on
back up the chain.

Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20230519215632.12343-11-shannon.nelson@amd.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>