PM / devfreq: Move cpubw device from msm_cpufreq to cpufreq governor

Enable the cpufreq governor for the cpubw device on all targets by:
- Adding the devfreq-cpufreq node for mapping CPU freq to cpubw
- Enabling the cpufreq governor configs when CPUBW config is selected
- Switching the default governor for cpubw device to "cpufreq"

Change-Id: Ic10b645123192ed13c66340f288d6a8553d6f251
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>