ifcvf/vDPA: fix misuse virtio-net device config size for blk dev

ifcvf/vDPA: fix misuse virtio-net device config size for blk dev

This commit fixes a misuse of virtio-net device config size issue
for virtio-block devices.

A new member config_size in struct ifcvf_hw is introduced and would
be initialized through vdpa_dev_add() to record correct device
config size.

To be more generic, rename ifcvf_hw.net_config to ifcvf_hw.dev_config,
the helpers ifcvf_read/write_net_config() to ifcvf_read/write_dev_config()

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Reported-and-suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Fixes: 6ad31d162a4e ("vDPA/ifcvf: enable Intel C5000X-PL virtio-block for vDPA")
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20211201081255.60187-1-lingshan.zhu@intel.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>