crypto: mips/chacha - wire up accelerated 32r2 code from Zinc

This integrates the accelerated MIPS 32r2 implementation of ChaCha
into both the API and library interfaces of the kernel crypto stack.

The significance of this is that, in addition to becoming available
as an accelerated library implementation, it can also be used by
existing crypto API code such as Adiantum (for block encryption on
ultra low performance cores) or IPsec using chacha20poly1305. These
are use cases that have already opted into using the abstract crypto
API. In order to support Adiantum, the core assembler routine has
been adapted to take the round count as a function argument rather
than hardcoding it to 20.

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