Mike,
I'm glad that we're both on the same page. Unfortunately it seems we're both stumped! I've escalated this LED blinking question to our developers. Hopefully they can shed some light on this situation and educate us on how to blink these LEDs! I really thought I'd see those GPIO expanders mentioned in the am335xevm.c file, but I didn't see any mention.
We had a similar setup on the OMAP-L138 EVM. You might want to take a look at board-da850-evm.c to see what was done there. In particular at line 899 is a i2c_board_info structure that has a couple of GPIO expanders at addresses 0x20 and 0x21. I'm hoping someone may already have a patch for this, but thought I'd mention this just in case.
Brad