crypto: gf128mul - make unselectable by user

There's no reason for users to select CONFIG_CRYPTO_GF128MUL, since it's
just some helper functions, and algorithms that need it select it.

Remove the prompt string so that it's not shown to users.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/Kconfig

@@ -159,13 +159,7 @@ config CRYPTO_MANAGER_EXTRA_TESTS
 endif	# if CRYPTO_MANAGER2
 
 config CRYPTO_GF128MUL
-	tristate "GF(2^128) multiplication functions"
-	help
-	  Efficient table driven implementation of multiplications in the
-	  field GF(2^128).  This is needed by some cypher modes. This
-	  option will be selected automatically if you select such a
-	  cipher mode.  Only select this option by hand if you expect to load
-	  an external module that requires these functions.
+	tristate
 
 config CRYPTO_NULL
 	tristate "Null algorithms"