[coreboot] CHIP_NAME history

[ron minnich]

I notice in bfb11bec3b3fec638adf864a9b9b2cff6671fed8 that CHIP_NAME is
gone.

I am glad to see it go, but I figured a quick note on history would help.

Back in the day, we had coreboot on systems with as little as 256 KiB of
memory. That was hard. One of the build options was to have CHIP_NAME
result in "", which saved the length of the string + 4 bytes (the pointer).
This was, on occasion, the difference between fitting an image or
overflowing. It mattered.

So the comment:
"    It was decided to remove this macro altogether, as it does not do
    anything special and incurs a maintenance burden."
is accurate now, since CHIP_NAME always returns the string.

But in the era in which CHIP_NAME was created, this comment is not correct.