crypto: md5 - Wrap library and add HMAC support

Reimplement crypto/md5.c on top of the new MD5 library functions.  Also
add support for HMAC-MD5, again just wrapping the library functions.

This closely mirrors crypto/sha1.c.

Link: https://lore.kernel.org/r/20250805222855.10362-7-ebiggers@kernel.org


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