C.H.I.P. computer power reductions (for nextthing CHIP boards)

Changes the core CPU clock from 1Ghz to 24Mhz (200Mhz also available in the code). Disables ALL of the video clocks and modules. Slows down the AHB and APB busses.

Gets down to about 110mA power draw on 5V input (instead of 250mA).

Tried changing the DRAM clock, but it only keeps running about 50% of the time after the change (not surprising), so this code is disabled.

todo:

• give command-line arguments as to what speed to run the CPU
• allow restoring everything to high power
• options for what parts of the chip to disable
• add led off
• figure out why 10% of the time the system behaves weirdly on wifi (24Mhz may just be too slow)
• write code to do most of the power reduction in the linux kernel in the idle loop