u-boot fix to charge empty battery

[Philipp Hug]

>> This causes u-boot to try to continue with the boot process and I guess
>> the neo uses more > 500mA and the PMU shuts it down.
>> Does this make more sense?
>>     
>
> Hmm, I thought this part worked at least in GTA02v6. GTA02v5 is more
> complex - with the battery completely drained, it may not even make it
> that far.
>
> What model do you have, GTA02v5 or GTA02v6 ?
>   
It should be a mass-production GTA02v6. Although I'm a bit confused
about the following message:
* Unrecognized hardware revision 0x305. Defaulting to GTA02v6.
* PCB rev: 0x305


After some more experimenting I found out, that when the neo is started
by plugging in USB power it sometimes generates a lowsys interrupt and
starts the shutdown-timer and shuts down after 8s.
To work around this I set the totrst to 1 in the OOCSHDWN register, now
it didn't shut down after 8s anymore.

Philipp