vdpa/mlx5: Clear and reinitialize software VQ data on reset

The hardware VQ configuration is mirrored by data in struct
mlx5_vdpa_virtqueue . Instead of clearing just a few fields at reset,
fully clear the struct and initialize with the appropriate default
values.

As clear_vqs_ready() is used only during reset, get rid of it.

Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Message-Id: <20240626-stage-vdpa-vq-precreate-v2-8-560c491078df@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>