nvmet: add tracing of reservation commands

Add tracing of reservation commands, including register, acquire,
release and report, and also parse the action and rtype to string
to make the trace log more human-readable.

Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>