crypto: riscv - add vector crypto accelerated ChaCha20

Add an implementation of ChaCha20 using the Zvkb extension. The
assembly code is derived from OpenSSL code (openssl/openssl#21923) that
was dual-licensed so that it could be reused in the kernel.
Nevertheless, the assembly has been significantly reworked for
integration with the kernel, for example by using a regular .S file
instead of the so-called perlasm, using the assembler instead of bare
'.inst', and reducing code duplication.

Signed-off-by: Jerry Shih <jerry.shih@sifive.com>
Co-developed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20240122002024.27477-6-ebiggers@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>