cipher:kyber: Apply changes from upstream for final FIPS 203.

* cipher/kyber-kdep.c (gen_matrix): Simplify for the case of
XOF_BLOCKBYTES%3 == 0.
(indcpa_keypair_derand): Add domain separation to key generation.

Manually apply upstream commits of:
ce492cd3d56bfca61bd941b6a73da3764e799aae
3c874cddd5fdaf4a7bd13f7e2e4d98a2a1eb8dc4
d5b791c0c601b543233daccbae2845c6197a9e77

• Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>