Activating LUKS2 device with OPAL support is multistep process.
1) read LR state
2) unlock LR
3) activate dm device
4) in case step 3) failed lock the device
if in step 1) the device was locked.
Otherwise, in case parallel activation happened on one device
the process that failed to map dm device (device already active)
could relock the LR afterwards and effectively break already active
device.
To avoid that we do steps 1) through 4) protected by exclusive
opal lock unique per data block device configured for use with
LUKS2 OPAL support.
It affects only HW OPAL locking range KEK.
After unlocking opal locking range we cache the key in kernel
so that we do not have to pass the key again for locking the
range later (the OPAL std requires key for lock command).
Unfortunately the key remains cached in kernel even after we
lock the range on purpose during crypt_deactivate* or crypt_suspend.
This had 2 side effects:
1) key remained in system memory even though the LUKS device was
inactive (and all keys should be erased from memory).
2) when system gets suspended the locking range got automatically
unlocked later after system resume because the key caching is used
primarly to automatically unlock locking ranges that got locked
after system suspend (due to power cut off on storage device).
Since kernel does not directly support dropping cached keys we achieve
that by overwritting the original key structure with empty one.
