lib/crypto: blake2s: Consolidate into single C translation unit

lib/crypto: blake2s: Consolidate into single C translation unit

As was done with the other algorithms, reorganize the BLAKE2s code so
that the generic implementation and the arch-specific "glue" code is
consolidated into a single translation unit, so that the compiler will
inline the functions and automatically decide whether to include the
generic code in the resulting binary or not.

Similarly, also consolidate the build rules into
lib/crypto/{Makefile,Kconfig}.  This removes the last uses of
lib/crypto/{arm,x86}/{Makefile,Kconfig}, so remove those too.

Don't keep the !KMSAN dependency.  It was needed only for other
algorithms such as ChaCha that initialize memory from assembly code.

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250827151131.27733-12-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>