hwrng: n2 - add device data descriptions

Since we're going to need to keep track of more than just one
attribute of the hardware, we'll change the use of the data field
from the match struct from a single flag to a struct pointer.
This patch adds the struct template and initial descriptions.

Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>