I saw this in the menuconfig for the empeg kernel. Could it be the answer, or is the change you mention also required? Check the screenshot... The help shows the following text:

CONFIG_CMDLINE:

On some architectures (EBSA110 and CATS), there is currently no way for the boot loader to pass arguments to the kernel. For these architectures, you should supply some command-line options at build time by entering them here. As a minimum, you should specify the memory size and the root device (e.g., mem=64M root=/dev/nfs).