powerpc/crypto: Enable the PFO-based encryption device

This patch adds the cas bits to advertise support for the Platform
Facilities Option (PFO) based encryption accelerator device. The nx
device driver provides support for this hardware feature.

Signed-off-by: Kent Yoder <key@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>