msm: clock-krait-8974: Add user voltage control

Change-Id: Ica9396347244a939c15b0601a1635c5daca02a48
arm/dts: msm8974: Add frequency steps up to 2.88GHz

Change-Id: I641f354eb8a378fc6bc33152399dcd291e9c2094
defconfig: Enable voltage control

Change-Id: I64a48bb43151e1d28c8432af5e7ee4a30b977cba
msm: acpuclock: Fix acpuclk_get_rate

acpuclk_get_rate() is broken, quick fix it by returning msm_cpufreq_get_freq
to avoid regressions.
msm: cpufreq: Don't try to call acpuclk_get_rate()

acpuclk_get_rate() is broken, so don't even try to call it as it will
invoke clk_get_rate() anyway.