nfs: add missing selections of CONFIG_CRC32

nfs.ko, nfsd.ko, and lockd.ko all use crc32_le(), which is available
only when CONFIG_CRC32 is enabled.  But the only NFS kconfig option that
selected CONFIG_CRC32 was CONFIG_NFS_DEBUG, which is client-specific and
did not actually guard the use of crc32_le() even on the client.

The code worked around this bug by only actually calling crc32_le() when
CONFIG_CRC32 is built-in, instead hard-coding '0' in other cases.  This
avoided randconfig build errors, and in real kernels the fallback code
was unlikely to be reached since CONFIG_CRC32 is 'default y'.  But, this
really needs to just be done properly, especially now that I'm planning
to update CONFIG_CRC32 to not be 'default y'.

Therefore, make CONFIG_NFS_FS, CONFIG_NFSD, and CONFIG_LOCKD select
CONFIG_CRC32.  Then remove the fallback code that becomes unnecessary,
as well as the selection of CONFIG_CRC32 from CONFIG_NFS_DEBUG.

Fixes: 1264a2f0 ("NFS: refactor code for calculating the crc32 hash of a filehandle")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Anna Schumaker <anna.schumaker@oracle.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>