dts: overclock CPU to 2.72Ghz

Conflicts:

	arch/arm/boot/dts/msm8974/msm8974-sec.dtsi
clock-krait/cpufreq: custom voltage control v1

* TODO: control only available frequencies (reverted from commit 3edcdc40708f46bc5d4df0961bb2f3030fa39c20)
cpufreq: OC up to 2.5GHz (Yank555.lu)

- added 2.34GHz, 2.42 GHz and 2.50GHz step
- max. voltage increased from 1100000 to 1200000 microVolt