target/riscv: Add itrigger support when icount is not enabled

target/riscv: Add itrigger support when icount is not enabled

When icount is not enabled, there is no API in QEMU that can get the
guest instruction number.

Translate the guest code in a way that each TB only has one instruction.
After executing the instruction, decrease the count by 1 until it reaches 0
where the itrigger fires.

Note that only when priviledge matches the itrigger configuration,
the count will decrease.

Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20221013062946.7530-2-zhiwei_liu@linux.alibaba.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>