lib/crypto: arm/sha512: Migrate optimized SHA-512 code to library

lib/crypto: arm/sha512: Migrate optimized SHA-512 code to library

Instead of exposing the arm-optimized SHA-512 code via arm-specific
crypto_shash algorithms, instead just implement the sha512_blocks()
library function.  This is much simpler, it makes the SHA-512 (and
SHA-384) library functions be arm-optimized, and it fixes the
longstanding issue where the arm-optimized SHA-512 code was disabled by
default.  SHA-512 still remains available through crypto_shash, but
individual architectures no longer need to handle it.

To match sha512_blocks(), change the type of the nblocks parameter of
the assembly functions from int to size_t.  The assembly functions
actually already treated it as size_t.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250630160320.2888-8-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>