[XS] Change in coreboot[main]: nb/haswell: Disable iGPU when dGPU is used

[Leah Rowe (Code Review)]

Attention is currently required from: Angel Pons, Arthur Heymans, Nico Huber.

Hello Angel Pons, build bot (Jenkins),

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/80717?usp=email

to look at the new patch set (#3).

The following approvals got outdated and were removed:
Verified+1 by build bot (Jenkins)

Change subject: nb/haswell: Disable iGPU when dGPU is used
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nb/haswell: Disable iGPU when dGPU is used

This is usually is handled by Haswell mrc.bin, disabling VGA
decode on the iGPU when a dGPU is installed. However, Broadwell
mrc.bin does not, so the iGPU and dGPU are both enabled.

This patch disables legacy VGA cycles for iGPU, under such
conditions. It has been tested on Broadwell mrc.bin when
using a graphics card on Dell OptiPlex 9020 SFF (currently
under review at this time of writing, submitted by Mate
Kukri).

This patch has also been tested when Haswell mrc.bin is used,
and there are seemingly no breaking changes caused by it.

Change-Id: I1df0a3aa42f8475b7741007bf3e28c2e089d916b
Signed-off-by: Leah Rowe 
---
M src/northbridge/intel/haswell/gma.c
1 file changed, 7 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/17/80717/3