Enable CryptoCell support for hardware keys.

Hardware keys are regular AES keys loaded into CryptoCell internal memory
via firmware, often from secure boot ROM or hardware fuses at boot time.

As such, they can be used for enc/dec purposes like any other key but
cannot (read: extremely hard to) be extracted since since they are not
available anywhere in RAM during runtime.

The mechanism has some similarities to s390 secure keys although the keys
are not wrapped or sealed, but simply loaded offline. The interface was
therefore modeled based on the s390 secure keys support.
Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>