build-setup: Add target for witherspoon-128
build-setup: Add target for witherspoon-128

Witherspoon-128 is a Power system under the witherspoon meta layer,
similar to witherspoon but with some hardware configuration differences
such as 128MB SPI NOR flash chips.

Change-Id: I9b3db8aaa8e0bed12244de6ac4d39f45185b2ecd
Signed-off-by: Adriana Kobylak <742cf4d8dead98b4cab50b088fd2a1406293c958@us.ibm.com>

openbmc/openbmc-build-scripts,openbmc/openbmc-build-scripts