crypto: mxs-dcp - Allow MXS_DCP to be used on MX6SL

MX6SL has the same DCP crypto block as in MX23/MX28, so allow it to be
built for ARCH_MXC.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>