crypto: lib/chacha - remove INTERNAL symbol and selection of CRYPTO

crypto: lib/chacha - remove INTERNAL symbol and selection of CRYPTO

Now that the architecture-optimized ChaCha kconfig symbols are defined
regardless of CRYPTO, there is no need for CRYPTO_LIB_CHACHA to select
CRYPTO.  So, remove that.  This makes the indirection through the
CRYPTO_LIB_CHACHA_INTERNAL symbol unnecessary, so get rid of that and
just use CRYPTO_LIB_CHACHA directly.  Finally, make the fallback to the
generic implementation use a default value instead of a select; this
makes it consistent with how the arch-optimized code gets enabled and
also with how CRYPTO_LIB_BLAKE2S_GENERIC gets enabled.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>