busfreq: Memory & internal voltage control

Plus permission change on other sysfs controls and addition of sampling rate.

We now have control of the defined OPPs and can parse, and change them.
Use it to modify the OPPs encapsulated memory interface voltages.

Internal voltage steps are dictated by the OPP freq steps, however, they are
stored and retrieved from the ASV table. Retrieve and change the INT steps
relative to their paired MIF steps by using the OPPs.