lib/crypto: sparc/md5: Migrate optimized code into library

Instead of exposing the sparc-optimized MD5 code via sparc-specific
crypto_shash algorithms, instead just implement the md5_blocks() library
function.  This is much simpler, it makes the MD5 library functions be
sparc-optimized, and it fixes the longstanding issue where the
sparc-optimized MD5 code was disabled by default.  MD5 still remains
available through crypto_shash, but individual architectures no longer
need to handle it.

Note: to see the diff from arch/sparc/crypto/md5_glue.c to
lib/crypto/sparc/md5.h, view this commit with 'git show -M10'.

Link: https://lore.kernel.org/r/20250805222855.10362-6-ebiggers@kernel.org


Signed-off-by: Eric Biggers <ebiggers@kernel.org>