target/riscv: rvk: add support for zbkx extension

- add xperm4 and xperm8 instructions

Signed-off-by: Weiwei Li <liweiwei@iscas.ac.cn>
Signed-off-by: Junqiang Wang <wangjunqiang@iscas.ac.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220423023510.30794-5-liweiwei@iscas.ac.cn>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/insn32.decode

@@ -776,6 +776,10 @@ clmulh     0000101 .......... 011 ..... 0110011 @r
 # *** RV32 extra Zbc Standard Extension ***
 clmulr     0000101 .......... 010 ..... 0110011 @r
 
+# *** RV32 Zbkx Standard Extension ***
+xperm4     0010100 .......... 010 ..... 0110011 @r
+xperm8     0010100 .......... 100 ..... 0110011 @r
+
 # *** RV32 Zbs Standard Extension ***
 bclr       0100100 .......... 001 ..... 0110011 @r
 bclri      01001. ........... 001 ..... 0010011 @sh