scsi: add tracing for SG_IO commands

Add tracepoints for SG_IO commands to allow for debugging
of SG_IO commands.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Message-Id: <20201116183114.55703-4-hare@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>