hwrng: nomadik - Add hardware RNG driver

The hardware random number generator by ST is used in both the Nomadik
8815 SoC and the U8500. It returns 16 bits every 400ns with automatic
delay if a read is issued too early. It depends on PLAT_NOMADIK.

Signed-off-by: Alessandro Rubini <rubini@unipv.it>
Acked-by: Andrea Gallo <andrea.gallo@stericsson.com>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>