affects all hiby targets, fiiom3k, and ibasso dx50/dx90
As well as deduplicating a small pile of code, this also implements
hysteresis so we're not doing a sysfs read/lookup multiple times
back-to-back every time the power management tick fires.
Change-Id: I2f7672acbb36341becf67e07960c24c681270d09
Provided by Roman Stolyarov
Integration, Refactoring, and Upstreaming by Solomon Peachy
X3II confirmed working by forum tester, X20 is nearly identical.
This includes bootloader, main firmware, and the flash image patcher.
Eventual Todo:
* Further refactor AGPTek Rocker & xduoo hiby bootloaders
* Further refactor AGPTek Rocker & xduoo hosted platform code
Change-Id: I34a674051d368efcc75d1d18c725971fe46c3eee
