hw/block/nvme: add support for the abort command

hw/block/nvme: add support for the abort command

Required for compliance with NVMe revision 1.3d. See NVM Express 1.3d,
Section 5.1 ("Abort command").

The Abort command is a best effort command; for now, the device always
fails to abort the given command.

Signed-off-by: Klaus Jensen <klaus.jensen@cnexlabs.com>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
Acked-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Message-Id: <20200706061303.246057-5-its@irrelevant.dk>