hw_random: add driver for atmel true hardware random number generator

For the IP block on 9g45/9g46/9m10/9m11.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Reviewed-by: Jamie Iles <jamie@jamieiles.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>