Let me explain all the DDR config's location. In uboot, take v2009.08 for example, i.MX6Q SabreSD board, the DDR config is in board/freescale/mx6q_sabresd/flash_header.S, which will initi DDR controller and DDR chip, then the DDR size is defined in include/configs/mx6q_sabresd.h, PHYS_SDRAM_1.
So you can take a look into Uboot board/freescale/mx6q_sabresd.c and review where is the print of the Size.
Thanks for the reply jamesbone.