hwrng: omap - Add device variant for SafeXcel IP-76 found in Armada 8K

This commits adds a device variant for Safexcel,EIP76 found in Marvell
Armada 8k. It defines registers mapping with the good offset and add a
specific initialization function.

Signed-off-by: Romain Perier <romain.perier@free-electrons.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>