u-boot fix to charge empty battery

[Philipp Hug]

> Yup. Given that one shouldn't have to spend time in wait_for_power
> very often (i.e., even if you run down your battery a lot, then you'll
> probably also make sure that you have a better power source than just
> 100mA), the general design principle there was more "survive the day"
> than "seize the day".
>
>   
the problem here is, that even 500mA is not enough to boot. at least 
that's what I experienced.
but maybe this was also only related to vsys going below it's threshold 
and initiating shutdown timer.

>> The idea in Qi is to defer anything fancy like the looping and flashing
>> and whatever until Linux is up, we just try to boot Linux with low power
>> (backlight off) and take care of it in there once rather than going on a
>> mission to really recreate Linux in U-Boot.
>>     
>
> By the way, do we know if we really stay in the 100mA envelope until
> the kernel can raise the current limit ?
>   
I think this would only work if we keep CPU at 200Mhz and also disable 
all other components. ( we can't start GSM early in u-boot anymore)
Better idea would probably be to charge to some level where we'll 
survive the boot process.