arm64: dts: marvell: add TRNG description for Armada 8K CP

This commits adds the devicetree description of the SafeXcel IP-76 TRNG
found in the two Armada CP110.

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