[Qemu-block] fix incorrect identify implementation in nvme

[Christoph Hellwig]

Third resent of this series after this didn't get picked up the
previous times.  The Qemu NVMe implementation mistakes the cns
field in the Identify command as a boolean.  This was never
true, and is actively harmful since NVMe1.1 (which the Qemu
device claims to support) supports more than two Identify variants.

We had to add a quirk in Linux to work around this behavior.