target/riscv: Enable native debug itrigger

target/riscv: Enable native debug itrigger

When QEMU is not in icount mode, execute instruction one by one. The
tdata1 can be read directly.

When QEMU is in icount mode, use a timer to simulate the itrigger. The
tdata1 may be not right because of lazy update of count in tdata1. Thus,
We should pack the adjusted count into tdata1 before read it back.

Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20221013062946.7530-4-zhiwei_liu@linux.alibaba.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>