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>