crypto: mips/chacha - import 32r2 ChaCha code from Zinc

This imports the accelerated MIPS 32r2 ChaCha20 implementation from the
Zinc patch set.

Co-developed-by: René van Dorst <opensource@vdorst.com>
Signed-off-by: René van Dorst <opensource@vdorst.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>