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

arch/riscv/Kconfig

@@ -578,6 +578,13 @@ config TOOLCHAIN_HAS_ZBB
 	depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
 	depends on AS_HAS_OPTION_ARCH
 
+# This symbol indicates that the toolchain supports all v1.0 vector crypto
+# extensions, including Zvk*, Zvbb, and Zvbc.  LLVM added all of these at once.
+# binutils added all except Zvkb, then added Zvkb.  So we just check for Zvkb.
+config TOOLCHAIN_HAS_VECTOR_CRYPTO
+	def_bool $(as-instr, .option arch$(comma) +zvkb)
+	depends on AS_HAS_OPTION_ARCH
+
 config RISCV_ISA_ZBB
 	bool "Zbb extension support for bit manipulation instructions"
 	depends on TOOLCHAIN_HAS_ZBB