GPU: Alter bus values

Add new low/high to conserve battery when possible and maintain performance
acpuclock: Lower a few more voltages

I've been running my undervoltage set for about 12 days now with
full stability. So it's pretty safe to say that they are safe enough to use
which is a good sign as my device no longer heats up during moderate/heavy
use as it did in previous voltage tables. I will be using this setup here on
out as they've proven beneficial.