acpi/nfit, libnvdimm: Add enable/update passphrase support for Intel nvdimms

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>