crypto: picoxcell - Allow driver to build COMPILE_TEST is enabled

Driver only has runtime but no build time dependency with ARCH_PICOXCELL.
So it can be built for testing purposes if COMPILE_TEST option is enabled.

This is useful to have more build coverage and make sure that the driver
is not affected by changes that could cause build regressions.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Acked-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>