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: NIlya Dryomov <ilya.dryomov@inktank.com>

net/ceph/Kconfig

@@ -3,6 +3,7 @@ config CEPH_LIB
 	depends on INET
 	select LIBCRC32C
 	select CRYPTO_AES
+	select CRYPTO_CBC
 	select CRYPTO
 	select KEYS
 	default n