beaglebone: changing cpu frequency

[Matt Thomas <matt%3am-software.com@localhost>]

I finally debugged the code I added to allow the changing of the
CPU frequency on the beaglebone (regardless of color).

Use sysctl to change it:

# sysctl -w machdep.frequency.current=1000      
cpu0: frequency changed from 550 MHz to 1000 MHz
machdep.frequency.current: 550 -> 1000

sysctl machdep.frequency.available will list the values you can pick from.

This is similar to how x86 powernow does it except it doesn't use
machdep.frequency.target.

I haven't tested it much but it seems to work for what little i've tested it.

I still need a good method to get the powersource from the tps65217pmic so
I can limit the frequencies when power is limited.

I'd appreciate if people could test it to make sure things really get faster
when you increase the cpu frequency. :)