nvme: add verbose error logging

Improves logging of NVMe errors.  If NVME_VERBOSE_ERRORS is configured,
a verbose description of the error is logged, otherwise only status
codes/bits is logged.

Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
[kch]: fix several nits, cosmetics, and trim down code.
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Alan Adamson <alan.adamson@oracle.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>