target/riscv: Use TARGET_FMT_lx for env->mhartid

target/riscv: Use TARGET_FMT_lx for env->mhartid

env->mhartid is currently casted to long before printed, which drops
the high 32-bit for rv64 on 32-bit host. Use TARGET_FMT_lx instead.

Signed-off-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230109152655.340114-1-bmeng@tinylab.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>