crypto: ixp4xx - Add device tree support

This makes the IXP4xx driver probe from the device tree
and retrieve the NPE and two queue manager handled used
to process crypto from the device tree.

As the crypto engine is topologically a part of the NPE
hardware, we augment the NPE driver to spawn the
crypto engine as a child.

The platform data probe path is going away in due time,
for now it is an isolated else clause.

Cc: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>