libceph: select CRYPTO_CBC in addition to CRYPTO_AES

We want "cbc(aes)" algorithm, so select CRYPTO_CBC too, not just
CRYPTO_AES.  Otherwise on !CRYPTO_CBC kernels we fail rbd map/mount
with

    libceph: error -2 building auth method x request

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>