crypto: caam - split RNG4 instantiation function

This patch splits the RNG4 state handle instantiation
function into two parts: one that handles the creation
of the descriptor which instructs the CAAM to perform
the instantiation of the state handle and another
function that performs the running of the said descriptor
using the DECO debug mechanism.

Signed-off-by: Alex Porosanu <alexandru.porosanu@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>