zen-tune: change default up_threshold and down_differential to be aggressive

On new CPU architectures, a high CPU frequency doesn't translate to signficantly
higher power draw when the CPU is idle.  Lets be more aggressive at scaling up
to mid and maximum frequencies as early as 30% CPU load.  After 60%, go for
maximum frequency.  Down sampling factor is still 10, so when above 60%, checks
happen at a factor of 10 less often decreasing context switching even further.