MFprojects/camlock r249541:
Give periph validity flag own periph reference.  That slightly simplifies
the release logic and covers hypothetical case if lock is dropped inside
the periph_oninval() method.
MFprojects/camlock r249542:
Remove ADA_FLAG_PACK_INVALID flag. Since ATA disks have no concept of media
change it only duplicates CAM_PERIPH_INVALID flag, so we can use last one.

Slightly cleanup DA_FLAG_PACK_INVALID use.