crypto: caam - Enable MXC devices to select CAAM driver in Kconfig

Allow CAAM to be selected in the kernel for Freescale i.MX devices if
ARCH_MXC is enabled.

Signed-off-by: Steve Cornelius <steve.cornelius@freescale.com>
Signed-off-by: Victoria Milhoan <vicki.milhoan@freescale.com>
Tested-by: Horia Geantă <horia.geanta@freescale.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>