lib/crypto: mldsa: Add FIPS cryptographic algorithm self-test

Since ML-DSA is FIPS-approved, add the boot-time self-test which is
apparently required.

Just add a test vector manually for now, borrowed from
lib/crypto/tests/mldsa-testvecs.h (where in turn it's borrowed from
leancrypto).  The SHA-* FIPS test vectors are generated by
scripts/crypto/gen-fips-testvecs.py instead, but the common Python
libraries don't support ML-DSA yet.

Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20260107044215.109930-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

Author: Eric Biggers