Change the first argument to disk_parsedev() to be a pointer to a struct devdesc *. This now gets filled in with a malloc'd structure that's returned to the caller that the caller is repsonsible for freeing. Most places in the tree passed in a malloc'd pointer anyway, and this moves knowledge of disk_devdesc more firmly into the disk.[ch] code. Sponsored by: Netflix Differential Revision: https://reviews.freebsd.org/D37335