RISC-V: add TOOLCHAIN_HAS_VECTOR_CRYPTO

Add a kconfig symbol that indicates whether the toolchain supports the
vector crypto extensions.  This is needed by the RISC-V crypto code.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20240122002024.27477-3-ebiggers@kernel.org


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>