[U-Boot] imximage: MAX_HW_CFG_SIZE_V2 too small for i.MX6D?

MAX_HW_CFG_SIZE_V2 is defined as 121 in tools/imximage.h, but I think the processor reference manual implies it can be larger (i.MX 6Dual/6Quad Applications Processor Reference Manual, Rev. 1, 04/2013).

In the section labelled "8.6.2 Device Configuration Data (DCD)" it says the DCD can be a maximum of 1768 bytes: "The maximum size of the DCD limited to 1768 bytes."

Have I misunderstood the link between the DCD size and MAX_HW_CFG_SIZE_V2? If so, where did the value of 121 for MAX_HW_CFG_SIZE_V2 come from?