Add support for enabling and updating passphrase on the Intel nvdimms.
The passphrase is the an encrypted key in the kernel user keyring.
We trigger the update via writing "update <old_keyid> <new_keyid>" to the
sysfs attribute "security". If no <old_keyid> exists (for enabling
security) then a 0 should be used.
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>