nvme: Add tracing

Add trace output for commands, errors, and undefined behavior.
Add guest error log output for undefined behavior.
Report invalid undefined accesses to MMIO.
Annotate unlikely error checks with unlikely.

Signed-off-by: Doug Gale <doug16k@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
