config: Set CONFIG_LIBCRC32C=y

Both nf_tables.ko and xfs.ko relying on libcrc32c.ko. But for some
reason, modprobe isn't able to automatically load libcrc32c.ko as a
dependency.

When I look at my host's modprobe.d config, I see some alias logic:

```
$ modprobe -c | rg crc32c
softdep ext4 pre: crc32c
softdep btrfs pre: crc32c
softdep bcachefs pre: crc32c
softdep libcrc32c pre: crc32c
alias cpu:type:x86,ven*fam*mod*:feature:*0094* crc32c_intel
alias crc32c crc32c_intel
alias crc32c crc32c_generic
alias crc32c_generic crc32c_generic
alias crc32c_intel crc32c_intel
alias crypto_crc32c crc32c_intel
alias crypto_crc32c crc32c_generic
alias crypto_crc32c_generic crc32c_generic
alias crypto_crc32c_intel crc32c_intel
alias symbol:crc32c libcrc32c
```

I imagine there are arch specific optimizations. And there's non trivial
logic to handle it.

Rather than figure it out, just build into the kernel libcrc32c.ko. Now
something like this will just work:

```
$ vmtest -k bzImage -- modprobe -d. -a nf_tables xfs
```

config/config

@@ -21,6 +21,7 @@ CONFIG_IKCONFIG=y
 CONFIG_IKCONFIG_PROC=y
 CONFIG_IPV6=y
 CONFIG_KEYS=y
+CONFIG_LIBCRC32C=y
 CONFIG_MODULE_SIG=y
 CONFIG_MODULE_SRCVERSION_ALL=y
 CONFIG_MODULE_UNLOAD=y