msm: devfreq_cpubw: Add devfreq driver for device bandwidth voting

This driver registers itself as a devfreq device that allows devfreq
governors to make IB/AB bandwidth votes. This driver allows the governors
to be agnostic of the bandwidth voting APIs, the number of master ports or
slave ports, the actual port numbers, the system topology, the available
frequencies, etc.

Change-Id: If055ddd580afd41f9668b111e6c09a047488b2e0
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
[Fix usage of 'QCOM' in Kconfig]
Signed-off-by: Jonathan Avila <avilaj@codeaurora.org>