RISC-V: fix check for zvkb with tip-of-tree clang

RISC-V: fix check for zvkb with tip-of-tree clang

LLVM commit 8e01042da9d3 ("[RISCV] Add missing dependency check for Zvkb
(#79467)") broke the check used by the TOOLCHAIN_HAS_VECTOR_CRYPTO
kconfig symbol because it made zvkb start depending on v or zve*.  Fix
this by specifying both v and zvkb when checking for support for zvkb.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240127090055.124336-1-ebiggers@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>