Well, Just for the heck of it I hardcoded the do_ram_command() and then I had to hardcode set_dram_row_attributes() just to see if I could get it to boot with the 512MB chip. Horray, it boots! But now there is a very strange Kernel panic everytime I try to boot Linux (see attached bootlog):
BUG: unable to handle kernel paging request at virtual address b71f2410
Well at least I now have some hope, and something to work towards:-)