target/riscv: add zicsr/zifencei to isa_string

Zicsr/Zifencei is not in 'I' since ISA version 20190608,
thus to fully express the capability of the CPU,
they should be exposed in isa_string.

Signed-off-by: Hongren (Zenithal) Zheng <i@zenithal.me>
Tested-by: Jiatai He <jiatai2021@iscas.ac.cn>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <YoTqwpfrodveJ7CR@Sun>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.c

@@ -1029,6 +1029,8 @@ static void riscv_isa_string_ext(RISCVCPU *cpu, char **isa_str, int max_str_len)
      *    extensions by an underscore.
      */
     struct isa_ext_data isa_edata_arr[] = {
+        ISA_EDATA_ENTRY(zicsr, ext_icsr),
+        ISA_EDATA_ENTRY(zifencei, ext_ifencei),
         ISA_EDATA_ENTRY(zfh, ext_zfh),
         ISA_EDATA_ENTRY(zfhmin, ext_zfhmin),
         ISA_EDATA_ENTRY(zfinx, ext_zfinx),