lib/crypto: blake2s: Always enable arch-optimized BLAKE2s code

When support for a crypto algorithm is enabled, the arch-optimized
implementation of that algorithm should be enabled too. We've learned
this the hard way many times over the years: people regularly forget to
enable the arch-optimized implementations of the crypto algorithms,
resulting in significant performance being left on the table.

Currently, BLAKE2s support is always enabled ('obj-y'), since random.c
uses it. Therefore, the arch-optimized BLAKE2s code, which exists for
ARM and x86_64, should be always enabled too. Let's do that.

Note that the effect on kernel image size is very small and should not
be a concern. On ARM, enabling CRYPTO_BLAKE2S_ARM actually *shrinks*
the kernel size by about 1200 bytes, since the ARM-optimized
blake2s_compress() completely replaces the generic blake2s_compress().
On x86_64, enabling CRYPTO_BLAKE2S_X86 increases the kernel size by
about 1400 bytes, as the generic blake2s_compress() is still included as
a fallback; however, for context, that is only about a quarter the size
of the generic blake2s_compress(). The x86_64 optimized BLAKE2s code
uses much less icache at runtime than the generic code.

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250827151131.27733-10-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>