crypto: tcrypt - rename CRYPTO_TEST to CRYPTO_BENCHMARK

tcrypt is actually a benchmarking module and not the actual tests.  This
regularly causes confusion.  Update the kconfig option name and help
text accordingly.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> # m68k
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>