ifdtool: fix flumap handling in chipsets prior ibex peak/5 series

The Upper Map section in the descriptor contains a database of flash
chips (VSCC Table). Its offset is located at a fixed offset from
the beginning of the image. ifdtool falsely calculates the offset
from the descriptor signature which has moved by 16 bytes with
step b of the Ibex Peak (5 series) chipset. This produces bogus
output for all chipsets older than that.

This patch corrects the behavior by calculating the offset of
flumap by adding 4096 - 256 - 4 to the start of the image.

Change-Id: I14f029fe702c129dfd8069a58fbd41113700f7ef
Signed-off-by: Stefan Tauner <stefan.tauner@gmx.at>
Reviewed-on: https://review.coreboot.org/27858
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
2 files changed