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.