virtio-blk: fix ZBD probe in kernels without ZBD support

When the kernel is built without support for zoned block devices,
virtio-blk probe needs to error out any host-managed device scans
to prevent such devices from appearing in the system as non-zoned.
The current virtio-blk code simply bypasses all ZBD checks if
CONFIG_BLK_DEV_ZONED is not defined and this leads to host-managed
block devices being presented as non-zoned in the OS. This is one of
the main problems this patch series is aimed to fix.

In this patch, make VIRTIO_BLK_F_ZONED feature defined even when
CONFIG_BLK_DEV_ZONED is not. This change makes the code compliant with
the voted revision of virtio-blk ZBD spec. Modify the probe code to
look at the situation when VIRTIO_BLK_F_ZONED is negotiated in a kernel
that is built without ZBD support. In this case, the code checks
the zoned model of the device and fails the probe is the device
is host-managed.

The patch also adds the comment to clarify that the call to perform
the zoned device probe is correctly placed after virtio_device ready().

Fixes: 95bfec41 ("virtio-blk: add support for zoned block devices")
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Message-Id: <20230330214953.1088216-3-dmitry.fomichev@wdc.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>