[U-Boot] various at91 patches to make some boards compilable again

[Reinhard Meyer]

Dear Alexander Stein,
> This patch series changes some at91 boards to SoC access and adds some defines
> to make the boards compilable again.
> Please note: All changes are untested!

Ok, I will look over them, and apply them in a test branch here, if they don't break
my board I think they can be mainlined, BUT you would need to be the maintainer of those
boards.

But if we receive no positive test reports in some time, those boards ultimately have to
be deleted.

I can only test on an at91sam9xe-ek.

Best Regards,

Reinhard