Print perf result at the end of simulation

[FanShupei]

Now t1/t1rocket will generate a perf.json at the end of simulation, currently only contains the number of total cycle numbers.

Here is the example of nix build .#t1.t1rocket.ip.vcs-emu.cases.codegen.vadd_vv.emu-result, in result/perf.json

{
    "total_cycles": 32444
}