Change in libgfxinit[master]: Add support to switch LSPCON modes

[Angel Pons (Code Review)]

Attention is currently required from: Martin Roth, Matt DeVillier, Angel Pons.
Hello Nico Huber, Patrick Georgi, Martin Roth, Matt DeVillier,

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

https://review.coreboot.org/c/libgfxinit/+/51133

to look at the new patch set (#11).

Change subject: Add support to switch LSPCON modes
......................................................................

Add support to switch LSPCON modes

LSPCON is a highly-cursed level shifter and protocol converter chip. It
is primarily used to convert DisplayPort into HDMI 2.0, since some Intel
iGPUs do not have native HDMI 2.0 support. The chip defaults to LS mode.

Add code to detect LSPCON chips and put them in protocol converter mode.
This way, the LSPCON behaves like a regular DisplayPort sink. This needs
to be done before any DPCD accesses, because the LSPCON does not respond
to DPCD accesses in level shifter mode.

Tested on Purism Librem Mini v1 (WHL-U), HDMI port can now light up.

Change-Id: Idfa9bdff47a6591000cd5092d64a4cd4f8dbdc8d
Signed-off-by: Angel Pons 
---
M common/Makefile.inc
A common/hw-gfx-dp_dual_mode.adb
A common/hw-gfx-dp_dual_mode.ads
M common/hw-gfx-gma-connector_info.adb
A common/hw-gfx-gma-dp_dual_mode.ads
5 files changed, 265 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/libgfxinit refs/changes/33/51133/11