cpufreq: use input boost only if u8500_hotplug is compiled in

the way u8500_hotlug driver is hardwired into governors makes it impossible to compile this kernel without it. And there's a good reason for it - hot(un)plugging cpu on suspend causes audio stuttering, which some people might find annoying. 

@cocafe I'm not sure if it's a good idea to use this driver by default when that thing is happening. Maybe add some kind of "enabled" parameter with false default value?

@zwliew have you had any issue with sound?

@zwliew is there any measured, proven evidence that hotplug in our case improves battery life? Because the more I think of it, the more it seems unnecesary to me - but that's just me thinking right now- testing is in progress.