[U-Boot] AM3517 SPL fails with CONFIG_DM enabled

[Adam Ford]

I am trying to add DM support in SPL along with device tree support
similar to how it's being done for the omap3_logic boards.
Unfortunately, I think something is going wrong in the initialization
with CONFIG_DM enabled for SPL because I get no text data, and it
doesn't appear to boot.

I tried enabling DM in SPL and using the older platdata method without
success.  I have disabled DM_SERIAL in SPL and tried enabling the
serial debug stuff, and I get nothing.  I don't have a debugger, so
it's a bit more difficult to troubleshoot.

The main difference between the am35 and omap3 is the memory
controller, and I've tried to model the am35 after the omap3 boards I
also maintain.  I was hoping someone might have any suggestions on how
to track down the issue.  As of right now, I have OF_CONTROL working
in U-Boot and with DM disabled in SPL, everything is good.

adam