crypto: omap-aes - Add support for multiple cores

Some SoCs like omap4/omap5/dra7 contain multiple AES crypto accelerator
cores. Adapt the driver to support this. The driver picks the last used
device from a list of AES devices.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
[t-kristo@ti.com: forward ported to 4.7 kernel]
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>