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

Instead of exposing the sparc-optimized SHA-512 code via sparc-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 sparc-optimized, and it fixes the
longstanding issue where the sparc-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 function from int to size_t.  The assembly function
actually already treated it as size_t.

Note: to see the diff from arch/sparc/crypto/sha512_glue.c to
lib/crypto/sparc/sha512.h, view this commit with 'git show -M10'.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250630160320.2888-14-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

lib/crypto/Kconfig

@@ -182,6 +182,7 @@ config CRYPTO_LIB_SHA512_ARCH
 	default y if MIPS && CPU_CAVIUM_OCTEON
 	default y if RISCV && 64BIT && RISCV_ISA_V && TOOLCHAIN_HAS_VECTOR_CRYPTO
 	default y if S390
+	default y if SPARC64
 
 config CRYPTO_LIB_SM3
 	tristate