crypto: api - Add softdep on cryptomgr

The crypto API requires cryptomgr to be present for probing to work
so we need a softdep to ensure that cryptomgr is added to the
initramfs.

This was usually not a problem because until very recently it was
not practical to build crypto API as module but with the recent
work to eliminate direct AES users this is now possible.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>