Make CRYPTO_CRC32C modular (bnc#762344)
    
    It was pulled in =y via CEPH_LIB=y, so we change the
    following options to =m:
    - CONFIG_CEPH_LIB
    - CONFIG_CRYPTO_CRC32C
    - CONFIG_LIBCRC32C
    
    Making it modular allows the Intel-optimized crc32c implementation
    to be loaded, improving performance of things like btrfs.