vDPA/ifcvf: fetch device feature bits when probe

vDPA/ifcvf: fetch device feature bits when probe

This commit would read and store device feature
bits when probe.

rename ifcvf_get_features() to ifcvf_get_hw_features(),
it reads and stores features of the probed device.

new ifcvf_get_features() simply returns stored
feature bits.

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210317094933.16417-6-lingshan.zhu@intel.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>