Add message when nvd disks are attached and detached.

Add message when nvd disks are attached and detached.

As part of this commit, add an nvme_strvis() function which borrows
heavily from cam_strvis().  This will allow stripping of
leading/trailing whitespace and also handle unprintable characters
in model/serial numbers.  This function goes into a new nvme_util.c
file which is used by both the driver and nvmecontrol.

Sponsored by:	Intel
Reviewed by:	carl
MFC after:	3 days