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

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

Instead of exposing the mips-optimized MD5 code via mips-specific
crypto_shash algorithms, instead just implement the md5_blocks() library
function.  This is much simpler, it makes the MD5 library functions be
mips-optimized, and it fixes the longstanding issue where the
mips-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/mips/cavium-octeon/crypto/octeon-md5.c
to lib/crypto/mips/md5.h, view this commit with 'git show -M10'.

Link: https://lore.kernel.org/r/20250805222855.10362-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>