cifs: Only select the required crypto modules

The sha256 and cmac crypto modules are only needed for SMB2+, so move
the select statements to config CIFS_SMB2. Also select CRYPTO_AES
there as SMB2+ needs it.

Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Steve French <sfrench@samba.org>