crypto: sa2ul - add device links to child devices

The child devices for sa2ul (like the RNG) have hard dependency towards
the parent, they can't function without the parent enabled. Add device
link for this purpose so that the dependencies are taken care of properly.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>