ARM: dts: msm: Move cpufreq node to top level 8974Pro dtsi

Any speedbins could be used in any 8974Pro variants.  It's not correct
to associate cpu frequency to a specific variant.  Move msm-cpufreq
node to top level 8974Pro dtsi so that all 8974Pro CPU will determine
its speed solely based on speedbin.

Change-Id: Icd7301e8a9daf8d130e6c650723ee3f9f3f994a5
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>